TECHNICAL FIELD
[0001] The present invention relates generally to rolling bearings, hub units, rolling contact
members, universal joints, torque transmission members for universal joints and methods
of producing the same, and particularly to rolling bearings, hub units and universal
joints that adopt for a component a sintered body containing β-sialon as a main component,
rolling contact members, torque transmission members for universal joints that are
formed of a sintered body containing β-sialon as a main component, and methods of
producing the same.
BACKGROUND ART
[0002] Silicon nitride, sialon and similar ceramics characteristically not only have a smaller
specific gravity and are more corrosive-resistant than steel but are also insulating.
Accordingly, if ceramics are adopted as a source material for a component of rolling
bearings (including hub units) including a race member and a rolling element, or a
component of a universal joint including a race member and a torque transmission member,
such as a race member, a rolling element, a torque transmission member, they can provide
bearings, universal joints and the like reduced in weight and also prevent rolling
bearings and universal joints from having short life as their components corrode and
are thus damaged or electrolytically corrode.
[0003] Furthermore, a hub unit, which is a type of rolling bearing, is often used in an
environment having a possibility of receiving moisture therein and hence having insufficient
lubricity. Ceramic rolling elements, race members and similar rolling contact members
are characteristically less damageable in such an insufficiently lubricating environment
as above. Accordingly, for example, a hub unit with a rolling contact member formed
with ceramics adopted as a source material can exhibit improved durability when it
is employed in an insufficiently lubricating environment.
[0004] Furthermore, a universal joint has a torque transmission member rolling and stopping
repeatedly on a surface of a race member, and between the torque transmission member
and the race member there is not sufficient oil film provided. Furthermore, a universal
joint is often used in an environment having a possibility of receiving moisture therein
and hence having insufficient lubricity. A ceramic torque transmission member is characteristically
less damageable in such an insufficiently lubricating environment as above. Accordingly,
for example, a universal joint with a torque transmission member formed with ceramics
adopted as a source material can exhibit improved durability when it is employed in
an insufficiently lubricating environment.
[0005] However, silicon nitride, sialon and similar ceramics require higher production cost
than steel, and adopting ceramics as a source material for components of rolling bearings
and universal joints disadvantageously increases their production costs.
[0006] In recent years, there has been developed a method of producing β-sialon, a type
of ceramics, inexpensively by adopting a production process including combustion synthesis
(Japanese Patent Laying-open No.
2004-91272 (Patent Document 1), Japanese Patent Laying-open No.
2005-75652 (Patent Document 2) and Japanese Patent Laying-open No.
2005-194154 (Patent Document 3)). This allows one to consider adopting β-sialon as a source material
for components of rolling bearings, universal joints and the like to produce them
inexpensively.
Patent Document 1: Japanese Patent Laying-open No. 2004-91272
Patent Document 2: Japanese Patent Laying-open No. 2005-75652
Patent Document 3: Japanese Patent Laying-open No. 2005-194154
DISCLOSURE OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0007] To adopt the above β-sialon as a source material for a component of a rolling bearing,
however, the component of the rolling bearing that is formed of β-sialon must have
a sufficient rolling contact fatigue life. Rolling contact fatigue life does not necessarily
match a member's fracture strength, and it cannot be said that a component of a rolling
bearing that is formed of β-sialon necessarily has a sufficient rolling contact fatigue
life. Thus it has not been easy either to ensure that a rolling bearing including
a component formed of β-sialon reliably has sufficient durability.
[0008] Furthermore, to adopt the above β-sialon as a source material for a torque transmission
member of a universal joint, however, the torque transmission member of the universal
joint that is formed of β-sialon must have sufficient durability. More specifically,
the universal joint has the torque transmission member sliding on a raceway and therewhile
rolling thereon as the universal joint operates. Accordingly the torque transmission
member receives rolling and sliding contact fatigue. Durability against rolling and
sliding contact fatigue does not necessarily match the torque transmission member's
fracture strength and the like, and it cannot be said that the universal joint with
the torque transmission member formed of β-sialon necessarily has sufficient durability
against rolling and sliding contact fatigue. Thus it has not been easy either to ensure
that the universal joint including the torque transmission member formed of β-sialon
reliably has sufficient durability.
[0009] Accordingly the present invention contemplates a rolling contact member serving as
a component of a rolling bearing, that is formed of a sintered β-sialon (a sintered
body containing β-sialon as a main component) inexpensive and capable of reliably
ensuring sufficient durability, and a method of producing the same, and a rolling
bearing (including a hub unit) including that rolling contact member. Furthermore,
the present invention also contemplates a torque transmission member for a universal
joint, that is formed of a sintered β-sialon (a sintered body containing β-sialon
as a main component) inexpensive and capable of reliably ensuring sufficient durability,
and a method of producing the same, and a universal joint that includes that torque
transmission member for the universal joint.
MEANS FOR SOLVING THE PROBLEMS
[0010] The present invention in one aspect provides a rolling bearing comprising: a race
member; and a plurality of rolling elements disposed in contact with the race member
on an annular raceway. The rolling element is configured of a sintered body that contains
as a main component a β-sialon represented by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity.
[0011] The present inventor has investigated in detail a relationship between the rolling
contact fatigue life of a rolling element containing β-sialon as a main component
and the β-sialon's composition, and as a result obtained the following finding and
arrived at the present invention.
[0012] More specifically, the above β-sialon can be produced to have a variety of compositions
having the above value of z (hereinafter referred to as value z) equal to or larger
than 0.1 by adopting a production process including combustion synthesis. In general,
rolling contact fatigue life is significantly affected by hardness, which hardly varies
for value z in a range that facilitates production, i.e., a range equal to or smaller
than 4.0. As what relationship is present between the rolling contact fatigue life
of a rolling element formed of a sintered body containing β-sialon as a main component
and value z has been investigated in detail, however, it has been found that value
z exceeding 3.5 significantly decreases the rolling element's rolling contact fatigue
life.
[0013] More specifically, value z in a range of 0.1 to 3.5 allows rolling contact fatigue
life to be substantially equivalent and when a rolling bearing with such value z is
operated for a period of time exceeding a predetermined period of time it has a rolling
element with a surface flaked and thus damaged. In contrast, value z exceeding 3.5
renders a rolling element wearable, resulting in significantly reduced rolling contact
fatigue life. That is, it has been revealed that a composition having value z of 3.5
serves as a boundary at which a rolling element formed of β-sialon has a varying damage
mode, and value z exceeding 3.5 significantly decreases rolling contact fatigue life.
Accordingly, ensuring that the rolling element formed of β-sialon reliably has sufficient
life requires value z equal to or smaller than 3.5.
[0014] As has been described previously, β-sialon can inexpensively be produced through
a production process including combustion synthesis. It has been found, however, that
value z less than 0.1 makes it difficult to perform combustion synthesis. Accordingly,
inexpensively producing a rolling element formed of a sintered body containing β-sialon
as a main component requires value z equal to or larger than 0.1.
[0015] The present invention in one aspect provides the rolling bearing that includes a
rolling element configured of a sintered body that contains as a main component a
β-sialon represented by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity. The present
invention in one aspect can thus provide a rolling bearing including a rolling element
formed of a sintered β-sialon inexpensive and capable of reliably ensuring sufficient
durability.
[0016] The present invention in another aspect provides a rolling bearing comprising: a
race member; and a plurality of rolling elements disposed in contact with the race
member on an annular raceway. The rolling element is configured of a sintered body
that contains as a main component a β-sialon represented by a compositional formula
of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an impurity.
[0017] The present invention in another aspect provides a rolling bearing basically similar
in configuration and in function and effect to the rolling bearing provided in one
aspect of the present invention as described above. However, the former is different
from the latter in that the sintered body contains a sintering additive, as the rolling
bearing's application and the like are considered. The rolling bearing in another
aspect of the present invention that adopts a sintering additive can facilitate decreasing
the sintered body's porosity and thus providing a rolling bearing including a rolling
element formed of a sintered β-sialon capable of reliably ensuring sufficient durability.
[0018] Note that the sintering additive can include at least one of an oxide, a nitride
and an oxynitride of magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti) and
a rare earth element. Furthermore, to achieve a function and effect equivalent to
that of the rolling bearing in one aspect of the present invention, it is desirable
that the sintering additive be equal to or smaller than 20% by mass of the sintered
body.
[0019] The present invention in one aspect provides a hub unit posed between a vehicular
wheel and a vehicular body and supporting the vehicular wheel relative to the vehicular
body rotatably. The present hub unit comprises: an outer member having an inner circumferential
surface having an annular raceway surface; an inner member disposed radially inner
than the outer member and having an annular raceway surface opposite to the raceway
surface of the outer member; and a plurality of rolling elements disposed in contact
with the raceway surface of the outer member and the raceway surface of the inner
member on an annular raceway. The rolling element is configured of a sintered body
that contains as a main component a β-sialon represented by a compositional formula
of S1
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity.
[0020] As well as the rolling bearing that the present invention provides in one aspect
as described above, the present invention in one aspect can provide a hub unit including
a rolling element formed of a sintered β-sialon inexpensive and capable of reliably
ensuring sufficient durability.
[0021] The present invention in another aspect provides a hub unit posed between a vehicular
wheel and a vehicular body and supporting the vehicular wheel relative to the vehicular
body rotatably. The hub unit comprises: an outer member having an inner circumferential
surface having an annular raceway surface; an inner member disposed radially inner
than the outer member and having an annular raceway surface opposite to the raceway
surface of the outer member; and a plurality of rolling elements disposed in contact
with the raceway surface of the outer member and the raceway surface of the inner
member on an annular raceway. The rolling element is configured of a sintered body
that contains as a main component a β-sialon represented by a compositional formula
of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an impurity.
[0022] As well as the rolling bearing that the present invention provides in another aspect
as described above, the present invention in another aspect can provide a hub unit
adopting a sintering additive to facilitate decreasing the sintered body's porosity
and thus providing a hub unit including a rolling element formed of a sintered β-sialon
capable of reliably ensuring sufficient durability.
[0023] The present invention in one aspect provides a rolling contact member in a rolling
bearing. The rolling contact member is one of a race member and a rolling element
disposed in contact with the race member on an annular raceway. The rolling contact
member is configured of a sintered body that contains as a main component a β-sialon
represented by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity. The rolling
contact member has a rolling contact surface serving as a surface contacting another
rolling contact member, and the rolling contact surface is included in a portion having
a high density layer higher in density than an inner portion.
[0024] The present invention in another aspect provides a rolling contact member in a rolling
bearing. The rolling contact member is one of a race member and a rolling element
disposed in contact with the race member on an annular raceway. The rolling contact
member is configured of a sintered body that contains as a main component a β-sialon
represented by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an impurity. The rolling contact member has a rolling contact surface serving as a
surface contacting another rolling contact member, and the rolling contact surface
is included in a portion having a high density layer higher in density than an inner
portion.
[0025] The present inventor has investigated in detail a relationship between the rolling
contact fatigue life of a rolling contact member containing β-sialon as a main component
and the rolling contact member's configuration, and as a result obtained the following
finding and arrived at the present invention.
[0026] More specifically, the present rolling contact member is configured of a sintered
body excellent in durability containing as a main component a β-sialon represented
by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5. When a sintered body containing β-sialon as a main
component, as described above, is used to produce a rolling contact member, its density
significantly affects rolling contact fatigue life, one of the most important durability
for the rolling contact member. The present rolling contact member is formed of a
sintered body containing β-sialon as a main component and has a raceway/rolling contact
surface included in a portion having a high density layer higher in density than an
inner portion. As a result the present invention can provide a rolling contact member
formed of a sintered body containing as a main component a β-sialon that is inexpensive
and capable of reliably ensuring sufficient durability as it achieves improved rolling
contact fatigue life.
[0027] Herein, a high density layer is a layer in a sintered body that is low in porosity
(or high in density), and can be inspected for example as follows: Initially, the
rolling contact member is cut along a cross section perpendicular to a surface of
the rolling contact member and the cross section is mirror-lapped. The mirror-lapped
cross section is then imaged through an optical microscope with oblique illumination
(a dark field) at a magnification for example of approximately 50-100 times, and stored
in an image equal to or larger than 300 dots per inch (DPI). In doing so, a portion
that is white in color is observed as a white color portion, which corresponds to
a portion high in porosity (or low in density). Accordingly, a portion having a white
color portion having a small area ratio is higher in density than a portion having
a white color portion having a large area ratio. An image processor is used to binarize
the stored image by a brightness threshold value and a white color portion's area
ratio is thus measured and therefrom the imaged portion's density can be obtained.
In other words, the present rolling contact member has a raceway/rolling contact surface
included in a portion having a high density layer having a white color portion having
a smaller area ratio than an inner portion does. Note that preferably the imaging
is done randomly at at least five locations and the area ratio is evaluated from an
average value thereof. Furthermore, the rolling contact member at an inner portion
has a white color portion having an area ratio for example equal to or larger than
15%.
[0028] Furthermore, to provide the rolling contact member with further increased rolling
contact fatigue life, it is preferable that the high density layer has a thickness
equal to or larger than 100 µm. Furthermore the sintering additive adopted in the
rolling contact member in another aspect as described above can be selected from at
least one of an oxide, a nitride and an oxynitride of magnesium (Mg), aluminum (Al),
silicon (Si), titanium (Ti) and a rare earth element. Furthermore, to achieve a function
and effect equivalent to that of the rolling contact member in one aspect of the present
invention, it is desirable that the sintering additive be equal to or smaller than
20% by mass of the sintered body.
[0029] In the above rolling contact member preferably when the high density layer is observed
in cross section with an optical microscope with oblique illumination, the layer exhibits
a portion observed as a portion white in color having an area ratio equal to or smaller
than 7%.
[0030] The high density layer improved in density to an extent allowing a white color portion
to have an area ratio equal to or smaller than 7% provides the rolling contact member
with further increased rolling contact fatigue life. The present rolling contact member
can thus achieve further increased rolling contact fatigue life.
[0031] In the above rolling contact member preferably the high density layer has a surface
included in a higher density layer higher in density than another portion of the high
density layer.
[0032] A higher density layer further higher in density and provided at a portion including
a surface of the high density layer can further enhance the rolling contact member's
durability against rolling contact fatigue and thus provide the rolling contact member
with further increased rolling contact fatigue life.
[0033] In the above rolling contact member preferably when the higher density layer is observed
in cross section with an optical microscope with oblique illumination, the layer exhibits
a portion observed as a portion white in color having an area ratio equal to or smaller
than 3.5%.
[0034] The higher density layer improved in density to an extent allowing a white color
portion to have an area ratio equal to or smaller than 3.5% provides the rolling contact
member with further increased rolling contact fatigue life. The present rolling contact
member can thus achieve further increased rolling contact fatigue life.
[0035] The present invention in still another aspect provides a rolling bearing comprising:
a race member; and a plurality of rolling elements disposed in contact with the race
member on an annular raceway. At least one of the race member and the rolling element
is the rolling contact member of the present invention as described above.
[0036] The present rolling bearing that includes the present rolling contact member can
be a rolling bearing including a rolling contact member formed of a sintered β-sialon
inexpensive and capable of reliably ensuring sufficient durability.
[0037] The present invention in one aspect provides a method of producing a rolling contact
member in a rolling bearing, the rolling contact member being one of a race member
and a rolling element disposed in contact with the race member on an annular raceway,
comprising the steps of: preparing a powdery source material that contains as a main
component a β-sialon represented by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity; shaping the
powdery source material generally into a geometry of the rolling contact member to
provide a shaped body; and sintering the shaped body at a pressure equal to or smaller
than 1 MPa.
[0038] The present invention in another aspect provides a method of producing a rolling
contact member in a rolling bearing, the rolling contact member being one of a race
member and a rolling element disposed in contact with the race member on an annular
raceway, comprising the steps of: preparing a powdery source material that contains
as a main component a β-sialon represented by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an impurity; shaping the powdery source material generally into a geometry of the
rolling contact member to provide a shaped body; and sintering the shaped body at
a pressure equal to or smaller than 1 MPa.
[0039] When a sintered body of ceramics is to be used to produce a rolling contact member,
a method is generally employed that adopts hot isostatic press (HIP), gas pressured
sintering (GPS), or similar pressure sintering (normally, a method sintering at a
pressure equal to or larger than 10 MPa) to reduce or prevent a defect reducing the
rolling contact member's rolling contact fatigue life. This conventional production
method can reduce the rolling contact member's porosity and thus produce a rolling
contact member high in density. The conventional production method adopting pressure
sintering, however, invites an increased production cost. Furthermore, the production
method adopting pressure sintering alters the rolling contact member at a surface
portion in material to cause an anomaly layer. This necessitates removing that anomaly
layer in a process for finishing the rolling contact member, which further increases
the rolling contact member's production cost. In contrast, if pressure sintering is
not adopted, the rolling contact member's porosity is increased and a defect is thus
caused and the rolling contact member's rolling contact fatigue life is decreased.
[0040] The present inventor has found that sintering a shaped body that contains β-sialon
as a main component at a pressure equal to or smaller than 1 MPa to produce a rolling
contact member can provide the rolling contact member at a portion that includes a
raceway/rolling contact surface (a surface) that is formed at a surface thereof with
a high density layer higher in density than an inner portion thereof. The present
method of producing a rolling contact member that includes the step of sintering a
shaped body that contains β-sialon as a main component at a pressure equal to or smaller
than 1 MPa can provide a portion that includes a raceway/rolling contact surface with
a high density layer while reducing/eliminating an increased production cost associated
with pressure sintering. Consequently the present method of producing a rolling contact
member can inexpensively produce a rolling contact member formed of a sintered β-sialon
capable of reliably ensuring sufficient durability.
[0041] Note that the step of sintering the shaped body is performed preferably at a pressure
equal to or larger than 0.01 MPa to reduce or prevent decomposition of β-sialon, and
more preferably at a pressure equal to or larger than the atmospheric pressure when
cost reduction is considered. Furthermore, to provide the high density layer while
reducing production cost, the step of sintering the shaped body is performed preferably
at a pressure equal to or smaller than 1 MPa.
[0042] In the method of producing a rolling contact member, as described above, preferably,
the step of sintering the shaped body includes sintering the shaped body in a range
of 1550°C to 1800°C.
[0043] If the shaped body is sintered at a temperature less than 1550°C, it is not sintered
to facilitate increasing it in density. Accordingly, the shaped body is sintered preferably
at a temperature equal to or higher than 1550°C and more preferably equal to or higher
than 1600°C. In contrast, if the shaped body is sintered at a temperature exceeding
1800°C, the β-sialon may have coarse crystal grains resulting in a sintered body having
poor mechanical characteristics. Accordingly, the shaped body is sintered preferably
at a temperature equal to or lower than 1800°C and more preferably equal to or lower
than 1750°C.
[0044] In the method of producing a rolling contact member, as described above, preferably,
the step of sintering the shaped body includes sintering the shaped body in one of
an atmosphere of an inert gas and an atmosphere of a gaseous mixture of nitrogen and
oxygen.
[0045] Sintering the shaped body in an atmosphere of an inert gas can reduce or prevent
the β-sialon's decomposition, microstructural variation, and the like. Furthermore,
sintering the shaped body in an atmosphere of a gaseous mixture of nitrogen and oxygen
allows a resultant sintered β-sialon to contain nitrogen and oxygen in a controlled
amount.
[0046] The method of producing a rolling contact member, as described above, preferably,
further includes the step of forming a surface of the shaped body before sintering
the shaped body.
[0047] The shaped body that has been sintered is significantly increased in hardness and
thus hard to work. Accordingly, for example sintering the shaped body and thereafter
extensively working the shaped body to finish it as a rolling contact member invites
an increased cost for producing the rolling contact member. In contrast, sintering
the shaped body after working it to allow a finishing step or the like to be done
such that the sintered shaped body is worked in a reduced amount allows a rolling
contact member to be produced at a reduced cost. In particular, a production method
adopting pressure sintering entails removing an anomaly layer, which entails working
a sintered body in a relatively large amount. Thus, such a step does not have a large
advantage. The present method of producing a rolling contact member adopts the step
of sintering a shaped body that is formed of β-sialon at a pressure equal to or smaller
than 1 MPa. This can reduce/eliminate an amount of working to remove an anomaly layer
and the step is thus significantly beneficial.
[0048] The method of producing a rolling contact member, as described above, preferably
further includes the step of working a surface of the sintered shaped body to remove
a portion including the surface, and the step of working removes the shaped body by
a thickness equal to or smaller than 150 µm.
[0049] The present method of producing a rolling contact member provides a portion including
a surface with a higher density layer aforementioned, and having a thickness of approximately
150 µm. Accordingly, when a sintered shaped body is to have a surface worked to remove
a portion including that surface, e.g., when the sintered shaped body undergoes a
finishing step, the finishing step that is done to remove the shaped body by a thickness
equal to or smaller than 150 µm allows the rolling contact member to have a raceway/rolling
contact surface with a higher density layer remaining therein. The step as described
above allows a rolling contact member to be produced with further improved rolling
contact fatigue life. Note that to ensure that the higher density layer remains, the
step more preferably removes the sintered shaped body by a thickness equal to or smaller
than 100 µm.
[0050] The present invention in one aspect provides a universal joint comprising: a race
member connected to a first shaft member; a torque transmission member arranged in
contact with the race member rollably on a surface of the race member; and a second
shaft member connected via the torque transmission member and the race member to the
first shaft member. The universal joint transmits rotation transmitted to one of the
first shaft member and the second shaft member about an axis to the other of the first
shaft member and the second shaft member. The torque transmission member is configured
of a sintered body that contains as a main component a β-sialon represented by a compositional
formula of S1
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity.
[0051] The present inventor has investigated in detail a relationship between the durability
of a torque transmission member that contains β-sialon as a main component against
rolling and sliding contact fatigue and the β-sialon's composition, and as a result
obtained the following finding and arrived at the present invention.
[0052] More specifically, the above β-sialon can be produced to have a variety of compositions
having the above value of z (hereinafter referred to as value z) equal to or larger
than 0.1 by adopting a production process including combustion synthesis. In general,
durability against rolling and sliding contact fatigue is significantly affected by
hardness, which hardly varies for value z in a range that facilitates production,
i.e., a range equal to or smaller than 4.0. As what relationship is present between
the durability of a torque transmission member formed of a sintered body containing
β-sialon as a main component against rolling and sliding contact fatigue and value
z has been investigated in detail, however, it has been found that value z exceeding
3.5 significantly decreases the torque transmission member's durability against rolling
and sliding contact fatigue.
[0053] More specifically, value z in a range of 0.1 to 3.5 allows durability against rolling
and sliding contact fatigue to be substantially equivalent and when a universal joint
is operated for a period of time exceeding a predetermined period of time the torque
transmission member has a surface flaked and thus damaged. In contrast, value z exceeding
3.5 renders the torque transmission member wearable, resulting in significantly reduced
durability against rolling and sliding contact fatigue. That is, it has been revealed
that a composition having value z of 3.5 serves as a boundary at which the torque
transmission member formed of β-sialon has a varying damage mode, and value z exceeding
3.5 significantly decreases durability against rolling and sliding contact fatigue.
Accordingly, ensuring that the torque transmission member formed of β-sialon reliably
has sufficient durability against rolling and sliding contact fatigue requires value
z equal to or smaller than 3.5.
[0054] As has been described previously, β-sialon can inexpensively be produced through
a production process including combustion synthesis. It has been found, however, that
value z less than 0.1 makes it difficult to perform combustion synthesis. Accordingly,
inexpensively producing a torque transmission member formed of a sintered body containing
β-sialon as a main component requires value z equal to or larger than 0.1.
[0055] The present invention in one aspect provides the universal joint that includes a
torque transmission member configured of a sintered body that contains as a main component
a β-sialon represented by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity. The present
invention in one aspect can thus provide a universal joint including a torque transmission
member formed of a sintered β-sialon inexpensive and capable of reliably ensuring
sufficient durability.
[0056] The present invention in another aspect provides a universal joint comprising: a
race member connected to a first shaft member; a torque transmission member arranged
in contact with the race member rollably on a surface of the race member; and a second
shaft member connected via the torque transmission member and the race member to the
first shaft member. The universal joint transmits rotation transmitted to one of the
first shaft member and the second shaft member about an axis to the other of the first
shaft member and the second shaft member. The torque transmission member is configured
of a sintered body that contains as a main component a β-sialon represented by a compositional
formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an impurity.
[0057] The present invention in another aspect provides a universal joint basically similar
in configuration and in function and effect to the universal joint provided in one
aspect of the present invention as described above. However, the former is different
from the latter in that the former contains a sintering additive, as the universal
joint's application and the like are considered. The universal joint in another aspect
of the present invention that adopts a sintering additive can facilitate decreasing
the sintered body's porosity and thus providing a universal joint including a torque
transmission member formed of a sintered β-sialon capable of reliably ensuring sufficient
durability.
[0058] Note that the sintering additive can include at least one of an oxide, a nitride
and an oxynitride of magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti) and
a rare earth element. Furthermore, to achieve a function and effect equivalent to
that of the universal joint in one aspect of the present invention, it is desirable
that the sintering additive be equal to or smaller than 20% by mass of the sintered
body.
[0059] The present invention in one aspect provides a torque transmission member for a universal
joint, provided in a universal joint between a race member connected to a first shaft
member and a second shaft member rollably and slidably and transmitting rotation transmitted
to one of the first shaft member and the second shaft member about an axis to the
other of the first shaft member and the second shaft member. The torque transmission
member is configured of a sintered body that contains as a main component a β-sialon
represented by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity. The torque
transmission member has a contact surface serving as a surface contacting another
member, and the surface is included in a portion having a high density layer higher
in density than an inner portion.
[0060] The present invention in another aspect provides a torque transmission member for
a universal joint, provided in a universal joint between a race member connected to
a first shaft member and a second shaft member rollably and slidably and transmitting
rotation transmitted to one of the first shaft member and the second shaft member
about an axis to the other of the first shaft member and the second shaft member.
The torque transmission member is configured of a sintered body that contains as a
main component a β-sialon represented by a compositional formula ofSi
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an impurity. The torque transmission member has a contact surface serving as a surface
contacting another member and the surface is included in a portion having a high density
layer higher in density than an inner portion.
[0061] The present inventor has investigated in detail a relationship between the durability
of a torque transmission member that is provided for a universal joint and contains
β-sialon as a main component against rolling and sliding contact fatigue and the torque
transmission member's configuration, and as a result obtained the following finding
and arrived at the present invention.
[0062] More specifically, the present torque transmission member for a universal joint is
configured of a sintered body excellent in durability, containing as a main component
a β-sialon represented by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5. When a sintered body containing β-sialon as a main
component, as described above, is used to produce a torque transmission member for
a universal joint, its density significantly affects durability against rolling and
sliding contact fatigue, one of the most important durability for the torque transmission
member for the universal joint. The present torque transmission member for a universal
joint is formed of a sintered body containing β-sialon as a main component and has
a contact surface included in a portion having a high density layer higher in density
than an inner portion. As a result the present invention can provide a torque transmission
member for a universal joint, that is formed of a sintered body containing as a main
component a β-sialon inexpensive and capable of reliably ensuring sufficient durability
as it achieves improved durability against rolling and sliding contact fatigue.
[0063] Herein, a high density layer is a layer in a sintered body that is low in porosity
(or high in density), and can be inspected for example as follows: Initially, the
torque transmission member for a universal joint is cut along a cross section perpendicular
to a surface of the torque transmission member for the universal joint and the cross
section is mirror-lapped. The mirror-lapped cross section is then imaged through an
optical microscope with oblique illumination (a dark field) at a magnification for
example of approximately 50-100 times, and stored in an image equal to or larger than
300 dots per inch (DPI). In doing so, a portion that is white in color is observed
as a white color portion, which corresponds to a portion high in porosity (or low
in density). Accordingly, a portion having a white color portion having a small area
ratio is higher in density than a portion having a white color portion having a large
area ratio. An image processor is used to binarize the stored image by a brightness
threshold value and a white color portion's area ratio is thus measured and therefrom
the imaged portion's density can be obtained. In other words, the present torque transmission
member for a universal joint has a contact surface included in a portion having a
high density layer having a white color portion having a smaller area ratio than an
inner portion does. Note that preferably the imaging is done randomly at at least
five locations and the area ratio is evaluated from an average value thereof. Furthermore,
the torque transmission member for the universal joint has at an inner portion a white
color portion having an area ratio for example equal to or larger than 15%.
[0064] Furthermore, to provide the torque transmission member for a universal joint with
further increased durability against rolling and sliding contact fatigue, it is preferable
that the high density layer has a thickness equal to or larger than 100 µm. Furthermore
the sintering additive adopted in the torque transmission member for a universal joint
in another aspect as described above can be selected from at least one of an oxide,
a nitride and an oxynitride of magnesium (Mg), aluminum (Al), silicon (Si), titanium
(Ti) and a rare earth element. Furthermore, to achieve a function and effect equivalent
to that of the torque transmission member for a universal joint in one aspect of the
present invention, it is desirable that the sintering additive be equal to or smaller
than 20% by mass of the sintered body.
[0065] In the above torque transmission member for a universal joint preferably when the
high density layer is observed in cross section with an optical microscope with oblique
illumination, the layer exhibits a portion observed as a portion white in color having
an area ratio equal to or smaller than 7%.
[0066] The high density layer improved in density to an extent allowing a white color portion
to have an area ratio equal to or smaller than 7% provides the torque transmission
member for a universal joint with further increased durability against rolling and
sliding contact fatigue. The present torque transmission member for a universal joint
can thus achieve further increased durability against rolling and sliding contact
fatigue.
[0067] In the above torque transmission member for a universal joint preferably the high
density layer has a surface included in a higher density layer higher in density than
another portion of the high density layer.
[0068] A higher density layer further higher in density and provided at a portion including
a surface of the high density layer can further enhance the torque transmission member
for a universal joint in durability against rolling and sliding contact fatigue.
[0069] In the above torque transmission member for a universal joint preferably when the
higher density layer is observed in cross section with an optical microscope with
oblique illumination, the layer exhibits a portion observed as a portion white in
color having an area ratio equal to or smaller than 3.5%.
[0070] The higher density layer improved in density to an extent allowing a white color
portion to have an area ratio equal to or smaller than 3.5% provides the torque transmission
member for a universal joint with further increased durability against rolling and
sliding contact fatigue.
[0071] The present invention in still another aspect provides a universal joint comprising:
a race member connected to a first shaft member; a torque transmission member arranged
in contact with the race member rollably and slidably on a surface of the race member;
and a second shaft member connected via the torque transmission member and the race
member to the first shaft member. The universal joint transmits rotation transmitted
to one of the first shaft member and the second shaft member about an axis to the
other of the first shaft member and the second shaft member. The torque transmission
member is the torque transmission member that is provided for a universal joint in
accordance with the present invention as described above.
[0072] The present universal joint that includes the present torque transmission member
for a universal joint, as described above, can provide a universal joint including
a torque transmission member formed of a sintered β-sialon inexpensive and capable
of reliably ensuring sufficient durability.
[0073] The present invention in one aspect provides a method of producing a torque transmission
member for a universal joint, provided in a universal joint between a race member
connected to a first shaft member and a second shaft member rollably and slidably
and transmitting rotation transmitted to one of the first shaft member and the second
shaft member about an axis to the other of the first shaft member and the second shaft
member, comprising the steps of: preparing a powdery source material that contains
as a main component a β-sialon represented by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity; shaping the
powdery source material generally into a geometry of the torque transmission member
for the universal joint to provide a shaped body; and sintering the shaped body at
a pressure equal to or smaller than 1 MPa.
[0074] The present invention in another aspect provides a method of producing a torque transmission
member for a universal joint, provided in a universal joint between a race member
connected to a first shaft member and a second shaft member rollably and slidably
and transmitting rotation transmitted to one of the first shaft member and the second
shaft member about an axis to the other of the first shaft member and the second shaft
member, comprising the steps of: preparing a powdery source material that contains
as a main component a β-sialon represented by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an impurity; shaping the powdery source material generally into a geometry of the
torque transmission member for the universal joint to provide a shaped body; and sintering
the shaped body at a pressure equal to or smaller than 1 MPa.
[0075] When a sintered body of ceramics is to be used to produce a torque transmission member
for a universal joint, a method is generally employed that adopts hot isostatic press
(HIP), gas pressured sintering (GPS), or similar pressure sintering (normally, a method
sintering at a pressure equal to or larger than 10 MPa) to reduce or prevent a defect
reducing the torque transmission member's durability against rolling and sliding contact
fatigue. This conventional production method can reduce the torque transmission member's
porosity and thus produce a torque transmission member high in density for a universal
joint. The conventional production method adopting pressure sintering, however, invites
an increased production cost. Furthermore, the production method adopting pressure
sintering alters the torque transmission member at a surface portion in material to
cause an anomaly layer. This necessitates removing that anomaly layer in a process
for finishing the torque transmission member, which further increases the cost for
producing the torque transmission member. In contrast, if pressure sintering is not
adopted, the torque transmission member's porosity is increased and a defect is thus
caused, and the torque transmission member is impaired in durability against rolling
and sliding contact fatigue.
[0076] The present inventor has found that sintering a shaped body that contains β-sialon
as a main component at a pressure equal to or smaller than 1 MPa to produce a torque
transmission member for a universal joint can provide the torque transmission member
at a portion that includes a contact surface (a surface) that is formed at a surface
thereof with a high density layer higher in density than an inner portion thereof.
The present method of producing a torque transmission member for a universal joint
that includes the step of sintering a shaped body that contains β-sialon as a main
component at a pressure equal to or smaller than 1 MPa can provide a portion that
includes a contact surface with a high density layer while reducing/eliminating an
increased production cost associated with pressure sintering. Consequently the present
method of producing a torque transmission member for a universal joint can inexpensively
produce a torque transmission member formed of a sintered β-sialon capable of reliably
ensuring sufficient durability for a universal joint.
[0077] Note that the step of sintering the shaped body is performed preferably at a pressure
equal to or larger than 0.01 MPa to reduce or prevent decomposition of β-sialon, and
more preferably at a pressure equal to or larger than the atmospheric pressure when
cost reduction is considered. Furthermore, to provide the high density layer while
reducing production cost, the step of sintering the shaped body is performed preferably
at a pressure equal to or smaller than 1 MPa.
[0078] In the method of producing a torque transmission member for a universal joint, as
described above, preferably, the step of sintering the shaped body includes sintering
the shaped body in a range of 1550°C to 1800°C.
[0079] If the shaped body is sintered at a temperature less than 1550°C, it is not sintered
to facilitate increasing it in density. Accordingly, the shaped body is sintered preferably
at a temperature equal to or higher than 1550°C and more preferably equal to or higher
than 1600°C. In contrast, if the shaped body is sintered at a temperature exceeding
1800°C, the β-sialon may have coarse crystal grains resulting in a sintered body having
poor mechanical characteristics. Accordingly, the shaped body is sintered preferably
at a temperature equal to or lower than 1800°C and more preferably equal to or lower
than 1750°C.
[0080] In the method of producing a torque transmission member for a universal joint, as
described above, preferably, the step of sintering the shaped body includes sintering
the shaped body in one of an atmosphere of an inert gas and an atmosphere of a gaseous
mixture of nitrogen and oxygen.
[0081] Sintering the shaped body in an atmosphere of an inert gas can reduce or prevent
the β-sialon's decomposition, microstructural variation, and the like. Furthermore,
sintering the shaped body in an atmosphere of a gaseous mixture of nitrogen and oxygen
allows a resultant sintered β-sialon to contain nitrogen and oxygen in a controlled
amount.
[0082] The method of producing a torque transmission member for a universal joint, as described
above, preferably, further includes the step of forming a surface of the shaped body
before sintering the shaped body.
[0083] The shaped body that has been sintered is significantly increased in hardness and
thus hard to work. Accordingly, for example sintering the shaped body and thereafter
extensively working the shaped body to finish it as a torque transmission member for
a universal joint invites an increased cost for producing the torque transmission
member for the universal joint. In contrast, sintering the shaped body after working
it to allow a finishing step or the like to be done such that the sintered shaped
body is worked in a reduced amount allows a torque transmission member for a universal
joint to be produced at a reduced cost. In particular, a production method adopting
pressure sintering entails removing an anomaly layer, which entails working a sintered
body in a relatively large amount. Thus, such a step does not have a large advantage.
The present method of producing a torque transmission member for a universal joint
adopts the step of sintering a shaped body formed of β-sialon at a pressure equal
to or smaller than 1 MPa. This can reduce/eliminate an amount of working to remove
an anomaly layer and the step is thus significantly beneficial.
[0084] The method of producing a torque transmission member for a universal joint, as described
above, preferably further includes the step of working a surface of the sintered shaped
body to remove a portion including the surface, and the step of working removes the
shaped body by a thickness equal to or smaller than 150 µm.
[0085] The present method of producing a torque transmission member for a universal joint
provides a portion including a surface with a higher density layer aforementioned,
and having a thickness of approximately 150 µm. Accordingly, when a sintered shaped
body is to have a surface worked to remove a portion including that surface, e.g.,
when the sintered shaped body undergoes a finishing step, the finishing step that
is done to remove the shaped body by a thickness equal to or smaller than 150 µm allows
the torque transmission member for the universal joint to have a contact surface with
a higher density layer remaining therein. The step as described above allows a torque
transmission member for a universal joint to be produced with further improved durability
against rolling and sliding contact fatigue. Note that to ensure that the higher density
layer remains, the step more preferably removes the sintered shaped body by a thickness
equal to or smaller than 100 µm.
EFFECTS OF THE INVENTION
[0086] As is apparent from the above description, the present rolling bearing, hub unit,
rolling contact member, and method of producing the same can provide a rolling contact
member formed of a sintered β-sialon inexpensive and capable of reliably ensuring
sufficient durability, and a method of producing the same, and a rolling bearing (including
a hub unit) including that rolling contact member. Furthermore, the present universal
joint, torque transmission member for a universal joint, and method of producing the
same can provide a torque transmission member for a universal joint that is formed
of a sintered β-sialon inexpensive and capable of reliably ensuring sufficient durability,
and a method of producing the same, and a universal joint that includes that torque
transmission member for the universal joint.
BRIEF DESCRIPTION OF THE DRAWINGS
[0087]
Fig. 1 is a schematic cross section of a configuration of a deep-grooved ball bearing
in a first embodiment.
Fig. 2 is a schematic cross section of a configuration of a thrust needle roller bearing
in an exemplary variation of the first embodiment.
Fig. 3 generally represents a method of producing a rolling bearing in the first embodiment.
Fig. 4 generally represents a method of producing a rolling element, as included in
the method of producing the rolling bearing in the first embodiment.
Fig. 5 is a schematic cross section of a configuration of a hub unit in a second embodiment.
Fig. 6 is an enlarged schematic partial cross section of a main portion of Fig. 1.
Fig. 7 is an enlarged schematic partial cross section of a main portion of a bearing
washer that the Fig. 2 thrust needle roller bearing includes.
Fig. 8 is an enlarged schematic partial cross section of a main portion of a needle
roller that the Fig. 2 thrust needle roller bearing includes.
Fig. 9 generally represents a method of producing a rolling contact member, as included
in a method of producing a rolling bearing in a third embodiment.
Fig. 10 is an enlarged schematic partial cross section of a main portion of Fig. 5.
Fig. 11 is a schematic cross section of a configuration of a constant velocity joint
(a fixed joint) in a fifth embodiment.
Fig. 12 is a schematic cross section taken along a line XII-XII shown in Fig. 11.
Fig. 13 is a schematic cross section of the Fig. 11 fixed joint forming an angle.
Fig. 14 generally represents a method of producing a universal joint in the fifth
embodiment.
Fig. 15 generally represents a method of producing a torque transmission member, as
included in the method of producing the universal joint in the fifth embodiment.
Fig. 16 is a schematic cross section of a configuration of a constant velocity joint
(a tripod joint) serving as a universal joint in a sixth embodiment.
Fig. 17 is a schematic cross section taken along a line XVII-XVII shown in Fig. 16.
Fig. 18 is an enlarged schematic partial cross section of a main portion of Fig. 11.
Fig. 19 is an enlarged schematic partial cross section of a main portion of Fig. 12.
Fig. 20 generally represents a method of producing a torque transmission member for
a universal joint, as included in a method of producing a universal joint in a seventh
embodiment.
Fig. 21 is an enlarged schematic partial cross section of a main portion of Fig. 17.
Fig. 22 is a photograph of a specimen for observation in cross section, as shot via
an optical microscope with oblique illumination.
Fig. 23 shows one example of binarizing the Fig. 22 photographic image by a brightness
threshold value using image processing software.
Fig. 24 shows a region subjected to an image process (a region to be evaluated) in
binarizing the Fig. 22 photographic image by the brightness threshold value using
the image processing software.
DESCRIPTION OF THE REFERENCE SIGNS
[0088] 1: deep-grooved ball bearing, 2: thrust needle roller bearing, 3: hub unit, 11: outer
ring, 11A: outer ring raceway surface, 11B: outer ring high density layer, 11C, 12C,
13C: inner portion, 11D: outer ring higher density layer, 12: inner ring, 12A: inner
ring raceway surface, 12B: inner ring high density layer, 12D: inner ring higher density
layer, 13: ball, 13A: ball rolling contact surface, 13B: ball high density layer,
13D: ball higher density layer, 14, 24, 39A, 39B: cage, 21: bearing washer, 21A: bearing
washer raceway surface, 21B: bearing washer high density layer, 21C, 23C: inner portion,
21D: bearing washer higher density layer, 23: needle roller, 23A: roller rolling contact
surface, 23B: roller high density layer, 23D: higher density layer, 31: outer ring,
31A1, 31A2, 32A, 33A: raceway surface, 31B: outer ring high density layer, 31C, 32C,
33C, 34C: inner portion, 31D: outer ring higher density layer, 32: hub ring, 32B:
hub ring high density layer, 32D: hub ring higher density layer, 33: inner ring, 33B:
inner ring high density layer, 33D: inner ring higher density layer, 34: ball, 34A:
ball rolling contact surface, 34B: ball high density layer, 34D: ball higher density
layer, 35: hub ring flange, 35A: hub ring through hole, 36: bolt, 37: outer ring flange,
37A: outer ring through hole, 38: fixing ring, 100: fixed joint, 111: inner race,
111A: inner race ball groove, 112: outer race, 112A: outer race ball groove, 113:
ball, 113A: ball rolling contact surface, 113B: ball high density layer, 113C: inner
portion, 113D: ball higher density layer, 114: cage, 115, 116: shaft, 200: tripod
joint, 221: tripod, 211: tripod shaft, 222: outer race, 222A: outer race groove, 223:
spherical roller, 223A: spherical roller rolling contact surface, 223B: spherical
roller high density layer, 223C: inner portion, 223D: spherical roller higher density
layer, 225, 226: shaft, 229: needle roller .
BEST MODES FOR CARRYING OUT THE INVENTION
[0089] Hereinafter reference will be made to the drawings to describe the present invention
in embodiments. In the figures, identical or corresponding components are identically
denoted and will not be described repeatedly.
First Embodiment
[0090] A deep-grooved ball bearing serving as a rolling bearing in a first embodiment of
the present invention will now be described hereinafter. With reference to Fig. 1,
a deep-grooved ball bearing 1 includes a race member implemented as an annular outer
ring 11, a race member implemented as an annular inner ring 12 arranged to be inner
than outer ring 11, and rolling elements implemented as a plurality of balls 13 arranged
between outer and inner rings 11 and 12 and held in an annular cage 14. Outer ring
11 has an inner circumferential surface having an outer ring raceway surface 11A and
inner ring 12 has an outer circumferential surface having an inner ring raceway surface
12A. Outer ring 11 and inner ring 12 are disposed such that inner ring raceway surface
12A and outer ring raceway surface 11A face each other. The plurality of balls 13
are held in a rollable manner on an annular raceway, with their rolling contact surfaces
13A in contact with inner ring raceway surface 12A and outer ring raceway surface
11 A, disposed at a predetermined pitch in the circumferential direction by means
of cage 14. By such a configuration, outer ring 11 and inner ring 12 of deep-grooved
ball bearing 1 can be rotated relative to each other.
[0091] Herein in the present embodiment the rolling element implemented as ball 13 is configured
of a sintered body that contains as a main component a β-sialon represented by a compositional
formula of S1
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity. The present
embodiment thus provides deep-grooved ball bearing 1 that is a rolling bearing including
a rolling element (ball 13) formed of a sintered β-sialon inexpensive and capable
of reliably ensuring sufficient durability. The impurity includes an unavoidably introduced
impurity including those derived from a source material or entering during the production
process.
[0092] Note that in the present embodiment the rolling element implemented as ball 13 may
be configured of a sintered body that contains as a main component a β-sialon represented
by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an unavoidably introduced impurity. The sintering additive helps to reduce the sintered
body in porosity and hence provide a rolling bearing including a rolling element formed
of a sintered β-sialon capable of reliably ensuring sufficient durability. The impurity
includes an unavoidably introduced impurity including those derived from a source
material or entering during the production process.
[0093] Hereinafter reference will be made to Fig. 2 to describe a thrust needle roller bearing
serving as a rolling bearing in an exemplary variation of the first embodiment.
[0094] With reference to Fig. 2, a thrust needle roller bearing 2 is basically similar in
configuration to deep-grooved ball bearing 1 described with reference to Fig. 1, except
that the former includes a race member and a rolling element different in configuration
than the latter. More specifically, thrust needle roller bearing 2 includes a pair
of bearing washers 21 in the form of a disk, serving as a race member arranged such
that their respective, one main surfaces face each other, a plurality of needle rollers
23 serving as a rolling element, and an annular cage 24. The plurality of needle rollers
23 are held in a rollable manner on an annular raceway, with their respective outer
circumferential surfaces or rolling contact surfaces 23A in contact with bearing washer
raceway surface 21A formed at the main surfaces of the pair of bearing washers 21
facing each other, disposed at a predetermined pitch in the circumferential direction
by means of cage 24. By such a configuration, the pair of bearing washers 21 of thrust
needle roller bearing 2 can be rotated relative to each other.
[0095] Herein in the present exemplary variation the rolling element implemented as needle
roller 23 corresponds to ball 13 as described above and is similar thereto in composition.
Thus the present exemplary variation provides thrust needle roller bearing 2 that
is a rolling bearing including a rolling element (needle roller 23) formed of a sintered
β-sialon inexpensive and capable of reliably ensuring sufficient durability.
[0096] Hereinafter will be described a method of producing a rolling bearing in the first
embodiment serving as one embodiment of the present invention.
[0097] With reference to Fig. 3, in the first embodiment, a rolling bearing is produced
in a method, as follows: Initially, a race member is produced in a race member production
step and a rolling element is produced in a rolling element production step. More
specifically the race member production step is performed to produce outer ring 11,
inner ring 12, bearing washer 21 and the like. The rolling element production step
is performed to produce ball 13, needle roller 23 and the like.
[0098] Then an assembly step is performed to combine the race member produced in the race
member production step and the rolling element produced in the rolling element production
step together to assemble a rolling bearing. More specifically, for example, outer
ring 11 and inner ring 12, and ball 13 are combined together to assemble deep-grooved
ball bearing 1. The rolling element production step is performed for example in accordance
with a method of producing a rolling element, as will be described hereinafter.
[0099] With reference to Fig. 4, in the first embodiment, a rolling element is produced
in a method as follows: Initially, a powdery β-sialon production step is performed
to produce powdery β-sialon represented by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5. The powdery β-sialon production step can be performed
for example with combustion synthesis adopted to produce powdery β-sialon inexpensively.
[0100] A mixture step is then performed to add a sintering additive to the powdery β-sialon
produced in the powdery β-sialon production step and mix them together. The mixture
step can be eliminated if the sintering additive is not added.
[0101] Then, with reference to Fig. 4, a shaping step is performed to shape the powdery
β-sialon or the mixture of the powdery β-sialon and the sintering additive generally
into the geometry of the rolling element. More specifically, the powdery β-sialon
or the mixture of the powdery β-sialon and the sintering additive is press-formed,
cast-molded, extrusion-formed, rolling-granulated, or similarly shaped to provide
a body shaped generally into a geometry of ball 13, needle roller 23 or the like.
[0102] A sintering step is then performed to heat and sinter the shaped body to produce
a sintered body generally having the geometry of ball 13, needle roller 23 or the
like. The sintering step may be performed at the normal atmospheric pressure, i.e.,
in the form of pressureless sintering. Alternatively, it may be done with hot press
(HP), hot isostatic press (HIP) or a similar sintering technique adopted. Furthermore
when the shaped body is sintered, it can be heated with: a heater; a microwave, a
millimeter wave or a similar electromagnetic wave; or the like.
[0103] Subsequently, with reference to Fig. 4, a finishing step is performed to work the
sintered body that has been produced in the sintering step to be finished to complete
a rolling element. More specifically, the sintered body produced in the sintering
step has a surface polished to complete a rolling element implemented as ball 13,
needle roller 23 or the like. Through the above steps a rolling element in the present
embodiment is completed. This rolling element is combined with outer ring 11 and inner
ring 12/bearing washer 21 that are separately prepared to assemble deep-grooved ball
bearing 1 or thrust needle roller bearing 2.
Second Embodiment
[0104] A second embodiment provides a hub unit, as will be described hereinafter. With reference
to Fig. 5, a hub unit 3 is basically similar in configuration and effect to deep-grooved
ball bearing 1 described with reference to Fig. 1, except that the former includes
a race member and a rolling element different in configuration than the latter. More
specifically, hub unit 3 is a device posed between a vehicular wheel and a vehicular
body and rotatably supporting the wheel relative to the body. Hub unit 3 includes
a race member implemented as an outer ring 31, a hub ring 32 and an inner ring 33,
and a rolling element implemented as a plurality of balls 34.
[0105] Outer ring 31, serving as an outer member, is an annular race member having an inner
circumferential surface provided with two rows of raceway surfaces 31A1, 31A2. Hub
ring 32, serving as an inner member, is a race member having a raceway surface 32A
opposite to one raceway surface 31A1 of outer ring 31 and disposed to have a portion
surrounded by outer ring 31. Furthermore, inner ring 33, serving as an inner member,
is an annular race member that has a raceway surface 33A opposite to the other raceway
surface 31A2 of outer ring 31, and is fitted in in contact with a portion of an outer
circumferential surface of hub ring 32, and fixed to hub ring 32 by a fixing ring
38 fitted in in contact with a portion of an outer circumferential surface of hub
ring 32.
[0106] The plurality of balls 34 are rotatably arranged on an annular raceway of a plurality
of (two) rows. One row is in contact with one raceway surface 31A1 of outer ring 31
and raceway surface 32A of hub ring 32 and arranged by an annular cage 39A in a circumferential
direction at a predetermined pitch. The other row is in contact with the other raceway
surface 31A2 of outer ring 31 and raceway surface 33A of inner ring 33 and arranged
by an annular cage 39B in a circumferential direction at a predetermined pitch. The
outer member implemented as outer ring 31 and the inner member implemented as hub
ring 32 and inner ring 33 can thus rotate relative to each other.
[0107] Furthermore, hub ring 32 has a hub ring flange 35 having a hub ring through hole
35A. Hub ring through hole 35A receives a bolt 36 to fix hub ring flange 35 and a
vehicular wheel (not shown) to each other. Outer ring 31 has an outer ring flange
37 having an outer ring through hole 37A. Outer ring through hole 37A receives a bolt
(not shown) to fix outer ring flange 37 and a suspension device (not shown) that is
fixed to the vehicular body to each other. Thus hub unit 3 is posed between the vehicular
wheel and the vehicular body to support the wheel relative to the body rotatably.
[0108] In other words, the present embodiment provides hub unit 3 that is a hub unit posed
between a vehicular wheel and a vehicular body to support the wheel relative to the
body rotatably. Hub unit 3 includes: an outer member implemented as outer ring 31
having an inner circumferential surface provided with annular raceway surface 31A1,
31 A2; an inner member implemented as hub ring 32 provided with annular raceway surface
32A opposite to raceway surface 31A1 of outer ring 31 and disposed with at least a
portion thereof surrounded by an inner circumferential surface of outer ring 31; and
an inner member implemented as inner ring 33 provided with annular raceway surface
33A opposite to raceway surface 31A2 of outer ring 31 and disposed with at least a
portion thereof surrounded by an inner circumferential surface of outer ring 31. Furthermore,
hub unit 3 includes a plurality of balls 34 arranged on an annular raceway and in
contact at a ball rolling contact surface 34A with outer ring 31 at raceway surfaces
31A1, 31A2 and hub ring 32 and inner ring 33 at raceway surfaces 32A, 33A.
[0109] Herein, with reference to Fig. 5, the present embodiment provides a rolling element
implemented as ball 34, which corresponds in the first embodiment to ball 13 and is
similarly configured. The present embodiment thus provides hub unit 3 that serves
as a rolling bearing including a rolling element (ball 34) formed of a sintered β-sialon
inexpensive and capable of reliably ensuring sufficient durability. Note that the
rolling bearing implemented in the second embodiment as hub unit 3 and the rolling
element implemented in the second embodiment as ball 34 that hub unit 3 includes can
be produced similarly as they are produced in the first embodiment.
Third Embodiment
[0110] The present invention in a third embodiment provides a rolling bearing and a rolling
contact member, as will be described hereinafter. With reference to Fig. 1, the third
embodiment provides a rolling bearing and a rolling contact member basically similar
in configuration and effect to those provided in the first embodiment. However, the
former has an additional feature, as follows:
[0111] With reference to Fig. 1, the third embodiment provides deep-grooved ball bearing
1 similar in configuration to the first embodiment, and thus having its outer ring
11 and inner ring 12 rotatable relative to each other.
[0112] Herein, with reference to Fig. 6, the present embodiment provides a rolling contact
member implemented as outer ring 11, inner ring 12 and ball 13 configured of a sintered
body that contains as a main component a β-sialon represented by a compositional formula
of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity. Furthermore,
outer ring 11, inner ring 12 and ball 13 have outer ring raceway surface 11A, inner
ring raceway surface 12A and ball rolling contact surface 13A, respectively, included
in a portion provided with an outer ring high density layer 11B, an inner ring high
density layer 12B and a ball high density layer 13B higher in density than inner portions
11C, 12C, 13C. When outer ring high density layer 11B, inner ring high density layer
12B and ball high density layer 13B are observed in cross section with an optical
microscope with oblique illumination, they exhibit a portion white in color, hereinafter
also referred to as a white color portion, having an area ratio equal to or smaller
than 7%. The present embodiment thus provides deep-grooved ball bearing 1 that serves
as a rolling bearing including a rolling contact member (outer ring 11, inner ring
12 and ball 13) formed of a sintered β-sialon inexpensive and capable of reliably
ensuring sufficient durability. The impurity includes an unavoidably introduced impurity
including those derived from a source material or entering during the production process.
[0113] Note that in the present embodiment the rolling contact member implemented as outer
ring 11, inner ring 12 and ball 13 may be configured of a sintered body that contains
β-sialon as a main component and has a remainder formed of a sintering additive and
an impurity. The sintering additive helps to reduce the sintered body in porosity
and hence provide a rolling bearing including a rolling contact member formed of a
sintered β-sialon capable of reliably ensuring sufficient durability. The impurity
includes an unavoidably introduced impurity including those derived from a source
material or entering during the production process.
[0114] Furthermore, with reference to Fig. 6, outer ring high density layer 11B, inner ring
high density layer 12B and ball high density layer 13B have surfaces, or outer ring
raceway surface 11A, inner ring raceway surface 12A and ball rolling contact surface
13A, respectively, included in a portion provided with an outer ring higher density
layer 11D, an inner ring higher density layer 12D and a ball higher density layer
13D further higher in density than another portion of outer ring high density layer
11B, inner ring high density layer 12B and ball high density layer 13B. When outer
ring higher density layer 11D, inner ring higher density layer 12D and ball higher
density layer 13D are observed in cross section with an optical microscope with oblique
illumination, they exhibit a white color portion having an area ratio equal to or
smaller than 3.5%. Outer ring 11, inner ring 12 and ball 13 are thus further improved
in durability against rolling contact fatigue and thus achieve further improved rolling
contact fatigue life.
[0115] The third embodiment in an exemplary variation provides a rolling bearing and a rolling
contact member, as will be described hereinafter. With reference to Fig. 2, the third
embodiment in the exemplary variation provides a rolling bearing and a rolling contact
member basically similar in configuration and effect to those in the exemplary variation
of the first embodiment. However, the former has an additional feature, as follows:
[0116] With reference to Fig. 2, the third embodiment in the exemplary variation provides
thrust needle roller bearing 2 similar in configuration to the exemplary variation
of the first embodiment, and thus having a pair of bearing washers 21 rotatable relative
to each other.
[0117] Herein, the present exemplary variation provides a rolling contact member implemented
as bearing washer 21 and needle roller 23, which correspond respectively to outer
ring 11 or inner ring 12 and ball 13 as described above and similarly have inner portions
21C, 23C, a high density layer (a bearing washer high density layer 21B, a roller
high density layer 23B) and a higher density layer (a bearing washer higher density
layer 21D, a roller higher density layer 23D). Thus the present exemplary variation
provides thrust needle roller bearing 2 that is a rolling bearing including a rolling
contact member (bearing washer 21, needle roller 23) formed of a sintered β-sialon
inexpensive and capable of reliably ensuring sufficient durability.
[0118] Hereinafter will be described a method of producing a rolling bearing and a rolling
contact member in the third embodiment serving as one embodiment of the present invention.
The third embodiment provides a method of producing a rolling bearing and a rolling
contact member that can be performed similarly as that in the first embodiment is
performed. However, the former method is different from the latter method in the method
of producing the rolling contact member.
[0119] With reference to Fig. 9, in the present embodiment, a rolling contact member is
produced in a method, as follows: Initially, powdery β-sialon is prepared in a powdery
β-sialon preparation step. The powdery β-sialon preparation step can be performed
for example with combustion synthesis adopted in a production step to produce powdery
β-sialon inexpensively.
[0120] A mixture step is then performed to add a sintering additive to the powdery β-sialon
prepared in the powdery β-sialon preparation step and mix them together. The mixture
step can be eliminated if the sintering additive is not added.
[0121] Then, with reference to Fig. 9, a shaping step is performed to shape the powdery
β-sialon or the mixture of the powdery β-sialon and the sintering additive generally
into the geometry of the rolling contact member. More specifically, the powdery β-sialon
or the mixture of the powdery β-sialon and the sintering additive is press-formed,
cast-molded, extrusion-formed, rolling-granulated, or similarly shaped to provide
a body shaped generally into the geometry of the rolling contact member implemented
as outer ring 11, inner ring 12, ball 13, bearing washer 21, needle roller 23 and
the like.
[0122] The step of forming before sintering is then performed to form a surface of the shaped
body to allow the shaped body that has been sintered to have a geometry closer to
that of a rolling contact member as desired. More specifically, green body forming
or a similar forming technique is used to shape the shaped body so that the shaped
body having been sintered can have a geometry closer to that of outer ring 11, inner
ring 12, ball 13, bearing washer 21, needle roller 23 or the like. The step of forming
before sintering can be eliminated if the shaping step provides a shaped body in a
condition allowing the shaped body that has been sintered to have a geometry close
to that of a rolling contact member as desired.
[0123] Then, with reference to Fig. 9, a sintering step is performed to sinter the shaped
body at a pressure equal to or smaller than 1 MPa. More specifically, the shaped body
is heated with a heater, a microwave, a millimeter wave or a similar electromagnetic
wave and thus sintered to provide a sintered body generally having a geometry of outer
ring 11, inner ring 12, ball 13, bearing washer 21, needle roller 23 or the like.
The shaped body is sintered by being heated in an atmosphere of an inert gas or that
of a gaseous mixture of nitrogen and oxygen to a range of 1550°C to 1800°C. The inert
gas can be helium, neon, argon, nitrogen or the like. In view of production cost reduction,
nitrogen is preferably adopted.
[0124] Then the sintered body produced in the sintering step has a surface worked to remove
a portion including that surface, i.e., it is worked for finish, to complete a rolling
contact member, i.e., a finishing step is performed. More specifically, the sintered
body produced in the sintering step has a surface polished to complete a rolling contact
member implemented as outer ring 11, inner ring 12, ball 13, bearing washer 21, needle
roller 23 and the like. Through the above steps the rolling contact member in the
present embodiment completes.
[0125] Herein, the sintering step provides a sintered body having at a portion from its
surface to a depth of approximately 500 µm a high density layer higher in density
than an inner portion and having a portion white in color, or a white color portion,
as observed in cross section with an optical microscope with oblique illumination,
having an area ratio equal to or smaller than 7%. Furthermore, the sintered body has
at a portion from its surface to a depth of approximately 150 µm a higher density
layer further higher in density than another portion of the high density layer and
having a portion white in color, or a white color portion, as observed in cross section
with an optical microscope with oblique illumination, having an area ratio equal to
or smaller than 3.5%. Accordingly in the finishing step the sintered body is removed
preferably by a thickness equal to or smaller than 150 µm in a portion that should
serve as a raceway/rolling contact surface in particular. This allows the higher density
layer to remain in a portion including outer ring raceway surface 11 A, inner ring
raceway surface 12A, ball rolling contact surface 13A, bearing washer raceway surface
21A and roller rolling contact surface 23A to provide the rolling contact member with
improved rolling contact fatigue life.
Fourth Embodiment
[0126] The present invention in a fourth embodiment provides a rolling bearing and a rolling
contact member, as will be described hereinafter. With reference to Fig. 5, the fourth
embodiment provides a rolling bearing implemented as a hub unit and its rolling contact
member basically similar in configuration and effect to those provided in the second
embodiment. However, the former has an additional feature, as follows:
[0127] With reference to Fig. 5, the fourth embodiment provides hub unit 3 similar in configuration
to the second embodiment, and thus capable of being posed between a vehicular wheel
and a vehicular body and rotatably supporting the wheel relative to the body.
[0128] Herein, with reference to Fig. 5 and Fig. 10, the present embodiment provides a rolling
contact member implemented as outer ring 31, hub ring 32 and inner ring 33, and ball
34, which correspond respectively to outer ring 11 and inner ring 12, and ball 13
of the third embodiment and similarly have inner portions 31C, 32C, 33C, 34C, a high
density layer (an outer ring high density layer 31B, a hub ring high density layer
32B, an inner ring high density layer 33B, a ball high density layer 34B) and a higher
density layer (an outer ring higher density layer 31D, a hub ring higher density layer
32D, an inner ring higher density layer 33D, a ball higher density layer 34D). Thus
the present embodiment provides hub unit 3 that is a rolling bearing including a rolling
contact member (outer ring 31, hub ring 32, inner ring 33, ball 34) formed of a sintered
β-sialon inexpensive and capable of reliably ensuring sufficient durability. Note
that the rolling bearing implemented in the fourth embodiment as hub unit 3 and the
rolling contact member implemented in the fourth embodiment as outer ring 31, hub
ring 32, inner ring 33, ball 34 that hub unit 3 includes in the fourth embodiment
can be produced similarly as they are produced in the third embodiment.
[0129] In the above embodiments the present rolling bearing and rolling contact member are
exemplified by a deep-grooved ball bearing, a thrust needle roller bearing and a hub
unit, and a rolling contact member that they include. The present rolling bearing
and rolling contact member, however, are not limited thereto. For example, the race
member may be a shaft, a plate, or the like allowing a rolling element to roll on
a surface thereof. In other words, the present rolling contact member corresponding
to the race member may be any member that has a raceway surface for rolling a rolling
element. Furthermore, the present rolling bearing may be a thrust ball bearing or
may be a radial roller bearing.
[0130] Furthermore, if in the present rolling bearing one of a race member and a rolling
element is the present rolling contact member, it is preferable that the rolling element
be the present rolling contact member, considering the cost for producing the rolling
bearing.
[0131] The present rolling bearing may have its race member formed of a material which is
not particularly limited. It may for example be steel, more specifically, Japanese
Industrial Standard (JIS) SUJ2 or a similar bearing steel, SCR420, SCM420 or a similar
carburizing steel. Furthermore, the present rolling bearing may have its race member
formed of a material of ceramics such as silicon nitride.
Fifth Embodiment
[0132] With reference to Fig. 11 to Fig. 13, the present invention in a fifth embodiment
provides a universal joint implemented as a fixed joint. Note that Fig. 11 corresponds
to a schematic cross section taken along a line XI-XI shown in Fig. 12.
[0133] With reference to Fig. 11, the fifth embodiment provides a fixed joint 100 including
a race member implemented as an inner race 111 coupled to a second shaft implemented
as a shaft 115, a race member implemented as an outer race 112 arranged to surround
the outer circumferential side of inner race 111 and coupled to a first shaft implemented
as a shaft 116, a torque transmission member implemented as a ball 113 arranged between
inner race 111 and outer race 112, and a cage 114 holding ball 113. Ball 113 is arranged
with a surface, or a ball rolling contact surface 113A, in contact with an inner race
ball groove 111A formed at the outer circumferential surface of inner race 111 and
an outer race ball groove 112A formed at the inner circumferential surface of outer
race 112, and is held by cage 114 to avoid falling off.
[0134] As shown in Fig. 11, inner race ball groove 111 A and outer race ball groove 112A
located at the outer circumferential surface of inner race 111 and the inner circumferential
surface of outer race 112, respectively, are formed in a curve (arc) with points A
and B equally spaced apart at the left and right on the axis passing through the center
of shafts 115 and 116 in a straight line from the joint center O on the axis as the
center of curvature. In other words, inner race ball groove 111 A and outer race ball
groove 112A are formed such that the trajectory of center P of ball 113 that rolls
in contact with inner race ball groove 111A and outer race ball groove 112A corresponds
to a curve (arc) with point A (inner race center A) and point B (outer race center
B) as the center of curvature. Accordingly, ball 113 is constantly located on the
bisector of an angle (Z AOB) with respect to the axis passing through the center of
shafts 115 and 116 even when the fixed joint forms an angle (when the fixed joint
operates such that the axes passing through the center of shafts 115 and 116 cross).
[0135] Fixed joint 100 operates, as will be described hereinafter. With reference to Figs.
11 and 12, when the rotation about the axis is transmitted to one of shafts 115 and
116 at fixed joint 100, this rotation is transmitted to the other of shafts 115 and
116 via ball 113 fitted in inner race ball groove 111 A and outer race ball groove
112A.
[0136] In the case where shafts 115 and 116 form an angle θ as shown in Fig. 13, ball 113
is guided by inner race ball groove 111A and outer race ball groove 112A with inner
race center A and outer race center B as the center of curvature to be held at a position
where its center P is located on the bisector of Z AOB. Since inner race ball groove
111A and outer race ball groove 112A are formed such that the distance from joint
center O to inner race center A is equal to the distance from joint center O to outer
race center B, the distance from center P of ball 113 to respective inner race center
A and outer race center B is equal. Thus, triangle OAP is congruent to triangle OBP.
As a result, the distances L from center P of ball 113 to shafts 115 and 116 are equal
to each other, and when one of shafts 115 and 116 rotates about the axis, the other
also rotates at constant velocity. Thus, fixed joint 100 can ensure constant velocity
even in the state where shafts 115 and 116 constitute an angle. Cage 114 serves, together
with inner race ball groove 111 A and outer race ball groove 112A, to prevent ball
113 from jumping out of inner race ball groove 111A and outer race ball groove 112A
when shafts 115 and 116 rotate, and also to determine joint center O of fixed joint
100.
[0137] In other words the fifth embodiment provides fixed joint 100 serving as a universal
joint, including a race member implemented as outer race 112 connected to a first
shaft member implemented as shaft 116, a torque transmission member implemented as
ball 113 arranged in contact with outer race 112 and rollably on a surface of outer
race ball groove 112A formed in outer race 112, and a second shaft member implemented
as shaft 115 connected to shaft 116 via ball 113 and outer race 112. Furthermore,
fixed joint 100 is a universal joint transmitting the rotation transmitted to one
of shaft 116 and shaft 115 about an axis to the other of shaft 116 and shaft 115.
[0138] The torque transmission member implemented as ball 113 is configured of a sintered
body that contains as a main component a β-sialon represented by a compositional formula
of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity. Thus the
present embodiment provides fixed joint 100 that is a universal joint including a
torque transmission member (ball 113) formed of a sintered β-sialon inexpensive and
capable of reliably ensuring sufficient durability. The impurity includes an unavoidably
introduced impurity including those derived from a source material or entering during
the production process.
[0139] Note that in the present embodiment the torque transmission member implemented as
ball 113 may be configured of a sintered body that contains as a main component a
β-sialon represented by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an unavoidably introduced impurity. The sintering additive helps to reduce the sintered
body in porosity and hence provide a universal joint including a torque transmission
member formed of a sintered β-sialon capable of reliably ensuring sufficient durability.
The impurity includes an unavoidably introduced impurity including those derived from
a source material or entering during the production process.
[0140] Hereinafter will be described a method of producing a universal joint in the fifth
embodiment serving as one embodiment of the present invention. With reference to Fig.
14, in the fifth embodiment, a universal joint is produced in a method, as follows:
Initially, a race member is produced in a race member production step and a torque
transmission member is produced in a torque transmission member production step. More
specifically the race member production step is performed to produce inner race 111,
outer race 112 and the like. The torque transmission member production step is performed
to produce ball 113 and the like.
[0141] Then an assembly step is performed to combine the race member produced in the race
member production step and the torque transmission member produced in the torque transmission
member production step together to assemble a universal joint. More specifically,
for example, inner race 111 and outer race 112, ball 113, and cage 114 separately
prepared and other components are combined together to assemble fixed joint 100. The
torque transmission member production step is performed for example in accordance
with a method of producing a torque transmission member for a universal joint, as
will be described hereinafter.
[0142] With reference to Fig. 15, in the fifth embodiment, a torque transmission member
for a universal joint is produced in a method as follows: Initially, a powdery β-sialon
production step is performed to produce powdery β-sialon represented by a compositional
formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5. The powdery β-sialon production step can be performed
for example with combustion synthesis adopted to produce powdery β-sialon inexpensively.
[0143] A mixture step is then performed to add a sintering additive to the powdery β-sialon
produced in the powdery β-sialon production step and mix them together. The mixture
step can be eliminated if the sintering additive is not added.
[0144] Then, with reference to Fig. 15, a shaping step is performed to shape the powdery
β-sialon or the mixture of the powdery β-sialon and the sintering additive generally
into the geometry of the torque transmission member. More specifically, the powdery
β-sialon or the mixture of the powdery β-sialon and the sintering additive is press-formed,
cast-molded, extrusion-formed, rolling-granulated, or similarly shaped to provide
a body shaped generally into a geometry of ball 113 or the like.
[0145] A sintering step is then performed to heat and sinter the shaped body to produce
a sintered body generally having the geometry of ball 113 or the like. The sintering
step may be performed at the normal atmospheric pressure, i.e., in the form of pressureless
sintering. Alternatively, it may be done with hot press (HP), hot isostatic press
(HIP) or a similar sintering technique adopted. Furthermore when the shaped body is
sintered, it can be heated with: a heater; a microwave, a millimeter wave or a similar
electromagnetic wave; or the like.
[0146] Subsequently, with reference to Fig. 15, a finishing step is performed to work the
sintered body that has been produced in the sintering step to be finished to complete
a torque transmission member. More specifically, the sintered body produced in the
sintering step has a surface polished to complete a torque transmission member implemented
as ball 113 or the like. Through the above steps a torque transmission member in the
present embodiment is completed. This torque transmission member is combined with
inner race 111 and outer race 112 that are separately prepared to assemble fixed joint
100.
Sixth Embodiment
[0147] The present invention in a sixth embodiment provides a universal joint implemented
as tripod joint configured as will be described hereinafter. With reference to Fig.
16 and Fig. 17, the sixth embodiment provides a tripod joint 200 basically similar
in configuration and effect to fixed joint 100 of the fifth embodiment. However, the
former is different from the latter in how the race member and the torque transmission
member are configured. More specifically, tripod joint 200 includes a tripod 221 that
has a tripod shaft 211 extending in a single plane in three directions and is connected
to a second shaft member implemented as a shaft 225, a race member implemented as
an outer race 222 arranged to surround tripod 221 and connected to a first shaft member
implemented as a shaft 226, and a torque transmission member implemented as an annular
spherical roller 223 attached to tripod shaft 211 via a needle roller 229 rollably
and having an outer circumferential surface having a spherical roller rolling contact
surface 223A in contact with a surface of an outer race groove 222A formed in an inner
circumferential surface of outer race 222.
[0148] Thus in tripod joint 200 when one of shafts 225, 226 receives rotation about an axis
the rotation can be transmitted via tripod 221, outer race 222 and spherical roller
223 to the other of shafts 225, 226 at a constant velocity and shafts 225, 226 can
also move relative to each other in an axial direction passing through the center
of shafts 225, 226.
[0149] In other words the sixth embodiment provides tripod joint 200 serving as a universal
joint, including a race member implemented as outer race 222 connected to a first
shaft member implemented as shaft 226, a torque transmission member implemented as
spherical roller 223 arranged in contact with outer race 222 and rollably on a surface
of outer race groove 222A formed in outer race 222, and a second shaft member implemented
as shaft 225 connected to shaft 226 via spherical roller 223 and outer race 222. Furthermore,
tripod joint 200 is a universal joint transmitting the rotation transmitted to one
of shaft 226 and shaft 225 about an axis to the other of shaft 226 and shaft 225.
[0150] The torque transmission member implemented as spherical roller 223 corresponds in
the fifth embodiment to ball 113 and is similarly configured. Thus the present embodiment
provides tripod joint 200 that is a universal joint including a torque transmission
member (spherical roller 223) formed of a sintered β-sialon inexpensive and capable
of reliably ensuring sufficient durability. Note that the universal joint implemented
in the sixth embodiment as tripod joint 200 and the torque transmission member implemented
in the sixth embodiment as spherical roller 223 that tripod joint 200 includes can
be produced similarly as they are produced in the fifth embodiment.
Seventh Embodiment
[0151] The present invention in a seventh embodiment provides a universal joint and a torque
transmission member for the universal joint. With reference to Fig. 11 to Fig. 13,
the seventh embodiment provides a universal joint and a torque transmission member
for the universal joint that are basically similar in configuration and effect to
those in the fifth embodiment. However, the former has an additional feature, as follows:
[0152] With reference to Fig. 11 to Fig. 13, the seventh embodiment provides fixed joint
100 having a configuration similar to the fifth embodiment. Thus when rotation about
an axis is transmitted to one of shafts 115 and 116, this rotation is transmitted
to the other of shafts 115 and 116 via ball 113 placed in inner race ball groove 111A
and outer race ball groove 112A, and even if shafts 115, 116 form an angle, constant
velocity can be ensured.
[0153] Herein, with reference to Fig. 18 and Fig. 19, the present embodiment provides a
torque transmission member for a universal joint, implemented as ball 113, which is
configured of a sintered body that contains as a main component a β-sialon represented
by a compositional formula of Si
6-ZAl
ZO
ZN
8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity. Furthermore,
ball 113 has a rolling contact surface, indicated as a ball rolling contact surface
113A, included in a portion provided with a ball high density layer 113B higher in
density than an inner portion 113C. When ball high density layer 113B is observed
in cross section with an optical microscope with oblique illumination, it exhibits
a portion white in color, hereinafter also referred to as a white color portion, having
an area ratio equal to or smaller than 7%. The present embodiment thus provides fixed
joint 100 that serves as a universal joint including a torque transmission member
(ball 113) formed of a sintered β-sialon inexpensive and capable of reliably ensuring
sufficient durability. The impurity includes an unavoidably introduced impurity including
those derived from a source material or entering during the production process.
[0154] Note that in the present embodiment the torque transmission member implemented as
ball 113 may be configured of a sintered body that contains β-sialon as a main component
and has a remainder formed of a sintering additive and an impurity. The sintering
additive helps to reduce the sintered body in porosity and hence provide a universal
joint including a torque transmission member formed of a sintered β-sialon capable
of reliably ensuring sufficient durability. The impurity includes an unavoidably introduced
impurity including those derived from a source material or entering during the production
process.
[0155] Furthermore, with reference to Fig. 18 and Fig. 19, ball high density layer 113B
has a surface, or ball rolling contact surface 113A, included in a portion provided
with a ball higher density layer 113D further higher in density than another portion
of ball high density layer 113B. When ball higher density layer 113D is observed in
cross section with an optical microscope with oblique illumination, it exhibits a
white color portion having an area ratio equal to or smaller than 3.5%. Ball 113 is
thus further improved in durability against rolling and sliding contact fatigue.
[0156] Hereinafter will be described a method of producing a universal joint and a torque
transmission member for the universal joint in the seventh embodiment serving as one
embodiment of the present invention. The seventh embodiment provides a method of producing
a universal joint and a torque transmission member for the universal joint that can
be performed similarly as that in the fifth embodiment is performed. However, the
former method is different from the latter method in the method of producing the torque
transmission member for the universal joint.
[0157] With reference to Fig. 20, in the present embodiment, a torque transmission member
for a universal joint is produced in a method, as follows: Initially, powdery β-sialon
is prepared in a powdery β-sialon preparation step. The powdery β-sialon preparation
step can be performed for example with combustion synthesis adopted in a production
step to produce powdery β-sialon inexpensively.
[0158] A mixture step is then performed to add a sintering additive to the powdery β-sialon
prepared in the powdery β-sialon preparation step and mix them together. The mixture
step can be eliminated if the sintering additive is not added.
[0159] Then, with reference to Fig. 20, a shaping step is performed to shape the powdery
β-sialon or the mixture of the powdery β-sialon and the sintering additive generally
into the geometry of the torque transmission member for the universal joint. More
specifically, the powdery β-sialon or the mixture of the powdery β-sialon and the
sintering additive is press-formed, cast-molded, extrusion-formed, rolling-granulated,
or similarly shaped to provide a body shaped generally into the geometry of the torque
transmission member implemented as ball 113 or the like for the universal joint.
[0160] The step of forming before sintering is then performed to form a surface of the shaped
body to allow the shaped body that has been sintered to have a geometry closer to
that of a torque transmission member as desired for a universal joint. More specifically,
green body forming or a similar forming technique is used to shape the shaped body
so that the shaped body having been sintered can have a geometry closer to that of
ball 113 or the like. The step of forming before sintering can be eliminated if the
shaping step provides a shaped body in a condition allowing the shaped body that has
been sintered to have a geometry close to that of a torque transmission member as
desired for a universal joint.
[0161] Then, with reference to Fig. 20, a sintering step is performed to sinter the shaped
body at a pressure equal to or smaller than 1 MPa. More specifically, the shaped body
is heated with a heater, a microwave, a millimeter wave or a similar electromagnetic
wave and thus sintered to provide a sintered body generally having a geometry of ball
113 or the like. The shaped body is sintered by being heated in an atmosphere of an
inert gas or that of a gaseous mixture of nitrogen and oxygen to a range of 1550°C
to 1800°C. The inert gas can be helium, neon, argon, nitrogen or the like. In view
of production cost reduction, nitrogen is preferably adopted.
[0162] Then the sintered body produced in the sintering step has a surface worked to remove
a portion including that surface, i.e., it is worked for finish, to complete a torque
transmission member for a universal joint, i.e., a finishing step is performed. More
specifically, the sintered body produced in the sintering step has a surface polished
to complete a torque transmission member implemented as ball 113 or the like for a
universal joint. Through the above steps the torque transmission member for the universal
joint in the present embodiment completes.
[0163] Herein, the sintering step provides a sintered body having at a portion from its
surface to a depth of approximately 500 µm a high density layer higher in density
than an inner portion and having a portion white in color, or a white color portion,
as observed in cross section with an optical microscope with oblique illumination,
having an area ratio equal to or smaller than 7%. Furthermore, the sintered body has
at a portion from its surface to a depth of approximately 150 µm a higher density
layer further higher in density than another portion of the high density layer and
having a portion white in color, or a white color portion, as observed in cross section
with an optical microscope with oblique illumination, having an area ratio equal to
or smaller than 3.5%. Accordingly in the finishing step the sintered body is removed
preferably by a thickness equal to or smaller than 150 µm in a portion that should
serve as a contact surface in particular. This allows the higher density layer to
remain in a portion including ball rolling contact surface 113A to provide the torque
transmission member for the universal joint with improved durability against rolling
and sliding contact fatigue.
Eighth Embodiment
[0164] The present invention in an eighth embodiment provides a universal joint and a torque
transmission member for the universal joint, as will be described hereinafter. With
reference to Fig. 16 and Fig. 17, the eighth embodiment provides a universal joint
and a torque transmission member for the universal joint basically similar in configuration
and effect to those provided in the sixth embodiment. However, the former has an additional
feature, as follows:
[0165] With reference to Fig. 16 and Fig. 17, the eighth embodiment provides tripod joint
200 having a configuration similar to the sixth embodiment. Thus when one of shafts
225, 226 receives rotation about the axis the rotation is transmitted via tripod 221,
outer race 222 and spherical roller 223 to the other of shafts 225, 226 at a constant
velocity and shafts 225, 226 can also move relative to each other in an axial direction
passing through the center of shafts 225, 226.
[0166] Herein, with reference to Fig. 17 and Fig. 21, the present embodiment provides a
torque transmission member for a universal joint, that is implemented as spherical
roller 223, which corresponds to ball 113 of the seventh embodiment and similarly
has an inner portion 223C, a high density layer (a spherical roller high density layer
223B) and a higher density layer (a spherical roller higher density layer 223D). Thus
the present embodiment provides tripod joint 200 that is a universal joint including
a torque transmission member for the universal joint (spherical roller 223) formed
of a sintered β-sialon inexpensive and capable of reliably ensuring sufficient durability.
Note that the universal joint implemented in the eighth embodiment as tripod joint
200 and the torque transmission member implemented in the eighth embodiment for the
universal joint as spherical roller 223 that tripod joint 200 includes can be produced
similarly as they are produced in the seventh embodiment.
[0167] Note that while in the above embodiment the present universal joint is exemplified
by a fixed joint and a tripod joint, the present universal joint is not limited thereto.
For example, the universal joint may be a double offset joint (DOJ), a free ring tripod
joint (FTJ), a cross groove joint (LJ) or the like.
[0168] The present universal joint may have its race member formed of a material which is
not particularly limited. For example it may specifically be Japanese Industrial Standard
(JIS) S53C or similar carbon steel, SCR420, SCM420 or a similar carburizing steel.
Furthermore, the present universal joint may have its race member formed of a material
of ceramics such as silicon nitride and sialon (including β-sialon).
Example 1
[0169] Hereinafter the present invention in an example 1 will be described. Rolling bearings
having rolling elements formed of sintered β-sialon having a variety of values z are
produced and tested to investigate the relationship between value z and rolling contact
fatigue life (durability). The test is conducted in the following procedure:
[0170] Initially, bearings to be tested are produced in a method, as will be described hereinafter.
Initially, combustion synthesis is employed to prepare powdery β-sialon having value
z in a range of 0.1-4 and rolling elements having value z of 0.1-4 are produced in
a method similar to that of producing a rolling element as described above in the
first embodiment with reference to Fig. 4. More specifically, they are produced in
a method, as follows: Initially, powder of β-sialon in the form of fine, submicron
grains and a sintering additive of aluminum oxide (AKP30 produced by Sumitomo Chemical
Co., Ltd) and yttrium oxide (yttrium oxide grade C produced by H. C. Starck) are wet-mixed
using a ball mill. Subsequently, a spray dryer is used to granulate the intermediate
product to produce granulated powder. The granulated powder is introduced in a die
and thus shaped to be a sphere, and furthermore, a cold isostatical press (CIP) is
employed to apply pressure to obtain a spherically shaped body.
[0171] Subsequently, the shaped body is preliminarily, pressurelessly sintered and thereafter
undergoes a HIP process at a pressure of 200 MPa in an atmosphere of nitrogen to produce
a sintered spherical body. Then, the sintered spherical body is lapped to be a 3/8
inch ceramic ball (JIS grade: G5). It is then combined with a separately prepared
bearing ring of bearing steel (JIS SUJ2) to produce a bearing of JIS type number 6206
(examples A-H of the present invention and comparative examples B-C). Furthermore,
for comparison, a rolling element formed of silicon nitride, i.e., a rolling element
having value z of 0 is also produced in a method similar to that for producing a rolling
element formed of β-sialon as described above, and is assembled similarly in a bearing
(a comparative example A).
[0172] The test is conducted in the following conditions: A bearing of JIS type number 6206
produced as described above undergoes a fatigue test such that it experiences a maximum
contact pressure Pmax of 3.2 GPa and is rotated at 2000 rpm, using a lubricant of
turbine oil VG68 (clean oil) circularly fed, and thus tested at room temperature.
A vibration detector is employed to monitor how the bearing in operation vibrates,
and after the bearing has a rolling element damaged when the bearing's vibration exceeds
a predetermined value, the test is stopped, and a period of time having elapsed since
the bearing started to operate until the test is stopped is recorded as the bearing's
life. Furthermore, after the test is stopped, the bearing is disassembled to inspect
how the rolling element is damaged.
Table 1
|
Comp. Ex. A |
Ex. A |
Ex. B |
Ex. C |
Ex. D |
Ex. E |
Ex. F |
Ex. G |
Ex. H |
Comp. Ex. B |
Comp. Ex. C |
Value z |
0 (Silicon Nitride) |
0.1 |
0.5 |
1 |
1.5 |
2 |
2.5 |
3 |
3.5 |
3.8 |
4 |
Life Ratio |
1 |
1.05 |
1.05 |
1.05 |
1.01 |
0.99 |
0.95 |
0.9 |
0.74 |
0.12 |
< 0.05 |
Type of Damage |
Flaked |
Flaked |
Flaked |
Flaked |
Flaked |
Flaked |
Flaked |
Flaked |
Flaked (Also Slightly Worn) |
Flaked (Also Worn) |
Worn |
[0173] Table 1 indicates a result of testing the present example. Table 1 indicates each
example of the present invention and each comparative example having a life represented
as a life ratio in comparison with comparative example A (silicon nitride) having
a life represented as 1 (one). Furthermore, how a rolling element is damaged is recorded
as "flaked" when it has a surface flaked, and as "worn" when it is not flaked and
has a surface worn and accordingly the test is stopped.
[0174] With reference to table 1, examples A-H of the present invention having value z equal
to or larger than 0.1 and equal to or smaller than 3.5 have life comparable to silicon
nitride (comparative example A). Furthermore, examples A-H of the present invention
also have damage similar to that of silicon nitride i.e., "flaked". In contrast, comparative
example B having value z exceeding 3.5 and thus deviating from the present invention's
range has a significantly reduced life and has a rolling element observed to be worn.
More specifically, it is considered that although comparative example B having value
z of 3.8 in the end has a rolling element flaked, the rolling element as it is worn
has an effect resulting in a significantly reduced life. Furthermore, comparative
example C having value z of 4 has a rolling element significantly worn in a significantly
short period of time, and thus has the rolling bearing significantly impaired in durability.
[0175] Thus for value z in a range of 0.1 to 3.5 a rolling bearing including a rolling element
formed of sintered sialon is substantially equivalent in durability to a rolling bearing
including a rolling element formed of sintered silicon nitride. For value z exceeding
3.5, in contrast, a rolling bearing has a rolling element wearable, which results
in a significantly reduced rolling contact fatigue life. Furthermore, it has been
clarified that increased value z changes a cause of damage to a rolling element formed
of β-sialon from "flaked" to "worn" and thus contributes to significantly reduced
rolling contact fatigue life. Thus it has been confirmed that value z in a range of
0.1 to 3.5 allows a rolling bearing to be provided that includes a rolling element
formed of a sintered β-sialon inexpensive and capable of reliably ensuring sufficient
durability.
[0176] Note that with reference to table 1 example H of the present invention having value
z exceeding 3, more specifically, value z of 3.5, has a rolling element slightly worn
and also provides a life shorter than examples A-G of the present invention. It can
be said therefrom that to more reliably ensure sufficient durability, value z equal
to or smaller than 3 is desirable.
[0177] Furthermore, it can be seen from the above test result that, to obtain durability
(or life) equivalent to that of a rolling element formed of silicon nitride, value
z equal to or smaller than 2 is preferable, and value z equal to or smaller than 1.5
is more preferable. Furthermore, when combustion synthesis is adopted in a production
process and accordingly, facilitating preparation of powdery β-sialon is considered,
value z equal to or larger than 0.5 is preferable, as a reaction caused by a self
heating effect can sufficiently be expected.
Example 2
[0178] Hereinafter the present invention in an example 2 will be described. A test is conducted
to inspect how the present rolling contact member and torque transmission member for
a universal joint have a high density layer and a higher density layer formed, as
seen in cross section. The test is conducted in the following procedure:
[0179] Initially, combustion synthesis is employed to prepare powdery β-sialon (product
name: Meramix, produced by Isman J Corporation) having a composition of Si
5AlON
7, and therefrom a specimen in the form of a cube having each side of approximately
10 mm is produced in a method similar to that of producing a rolling contact member
and a torque transmission member for a universal joint, as described in the third
and seventh embodiments with reference to Fig. 9 and Fig. 20. More specifically, it
is produced in a method, as follows: Initially, powder of β-sialon in the form of
fine, submicron grains and a sintering additive of aluminum oxide (AKP30 produced
by Sumitomo Chemical Co., Ltd) and yttrium oxide (yttrium oxide grade C produced by
H. C. Starck) are wet-mixed using a ball mill. Subsequently, a spray dryer is used
to granulate the intermediate product to produce granulated powder. The granulated
powder is introduced in a die and thus shaped to have a predetermined geometry, and
furthermore, a cold isostatical press (CIP) is employed to apply pressure to obtain
a shaped body. Subsequently the shaped body is heated in an atmosphere of nitrogen
of a pressure of 0.4 MPa to 1650°C and thus sintered to produce the above cubic specimen.
[0180] Subsequently, the specimen is cut and the cut surface is lapped with a diamond lap
and thereafter mirror-lapped with a chromium oxide lap to obtain a cross section including
a center of the cube for observation. The cross section is observed with an optical
microscope (Microphoto-FXA produced by Nikon Corporation) with oblique illumination
and imaged in an instant photograph (FP-100B produced by FUJIFILM Corporation) of
a magnification of 50 times. Subsequently, the obtained photograph's image is taken
in via a scanner (with a resolution of 300 dpi) to a personal computer. Image processing
software (WinROOF produced by Mitani Corporation) is used to perform a binarization
process by a brightness threshold value (in the present example, a binarizing separation
threshold value: 140) to measure a white color portion for an area ratio.
[0181] The test provides a result, as described hereinafter. Note that Fig. 22 shows a photograph
having an upper side showing a side of a specimen that is closer to a surface thereof,
and a top end corresponding to the surface.
[0182] With reference to Fig. 22 and Fig. 23, it can be seen that a specimen in the present
example produced in a method similar to that of producing the present rolling contact
member and torque transmission member for a universal joint has in a portion including
a surface a layer having a white color portion less than an inner portion does, and
as shown in Fig. 24, a shot photograph's image is divided in accordance with a distance
from an outermost surface of the specimen into three regions (i.e., a region from
the outermost surface to a depth of 150 µm, a region that exceeds 150 µm and does
not exceed 500 µm, and a region that exceeds 500 µm and does not exceed 800 µm), and
each region is subjected to image analysis to calculate a white color portion for
area ratio. A result shown in table 2 is obtained. In table 2, the Fig. 24 each shown
region serves as one field of view, and from five randomly shot photographs, five
fields of view are obtained. For each field, a white color portion is measured for
area ratio, and their average and maximum values are indicated.
Table 2
|
Depth from Outermost Surface (µm) |
Area Ratio of White Color Portion (%) |
Ave. of 5 Fields of View |
Max. of 5 Fields of View |
1) Higher Density Layer |
150 |
1.2 |
3.5 |
2) High Density Layer |
150-500 |
3.7 |
7.0 |
3) Inner Portion |
> 500 |
18.5 |
22.4 |
[0183] With reference to table 2, the present example provides a white color portion having
an area ratio of 18.5% for an inner portion, and, in contrast, 3.7% for the region
having a depth equal to or smaller than 500 µm from a surface, and 1.2% for the region
having a depth equal to or smaller than 150 µm from the surface. It has been confirmed
therefrom that a specimen produced in the present example in a method similar to that
of producing the present rolling contact member and torque transmission member for
a universal joint has in a portion including a surface a high density layer and a
higher density layer having a white color portion less than an inner portion does.
Example 3
[0184] Hereinafter the present invention in an example 3 will be described. A test is conducted
to confirm the present rolling contact member's rolling contact fatigue life. The
test is conducted in the following procedure:
[0185] Initially, a bearing to be tested is produced in a method, as will be described hereinafter.
Initially, combustion synthesis is employed to prepare powdery β-sialon (product name:
Meramix, produced by Isman J Corporation) having a composition of Si
5AlON
7, and therefrom a 3/8 inch ceramic ball having a diameter of 9.525 mm is produced
in a method similar to that of producing a rolling contact member, as described in
the third embodiment with reference to Fig. 9. More specifically, it is produced in
a method, as follows: Initially, powder of β-sialon in the form of fine, submicron
grains and a sintering additive of aluminum oxide (AKP30 produced by Sumitomo Chemical
Co., Ltd) and yttrium oxide (yttrium oxide grade C produced by H. C. Starck) are wet-mixed
using a ball mill. Subsequently, a spray dryer is used to granulate the intermediate
product to produce granulated powder. The granulated powder is introduced in a die
and thus shaped to be a sphere, and furthermore, a cold isostatical press (CIP) is
employed to apply pressure to obtain a spherically shaped body.
[0186] Then the shaped body is subjected to green body forming so that after it is sintered
it has a predetermined working thickness. Subsequently the shaped body is heated in
an atmosphere of nitrogen of a pressure of 0.4 MPa to 1650°C and thus sintered to
produce a sintered spherical body. Then the sintered spherical body is lapped to be
a 3/8 inch ceramic ball (a rolling element; JIS grade: G5). It is then combined with
a separately prepared bearing ring of bearing steel (JIS SUJ2) to produce a bearing
of JIS type number 6206. Herein, the sintered spherical body is lapped to have a thickness
(or a working thickness) removed in 8 levels to produce 8 types of bearings (examples
A-H of the present invention). In contrast, for comparison, silicon nitride and a
sintering additive are used to provide a powdery source material which is in turn
pressure-sintered to provide a sintered spherical body (EC 141 produced by NGK Spark
Plug Co. Ltd.) which is in turn lapped, similarly as described above, and combined
with a separately prepared bearing ring of bearing steel (JIS SUJ2) to produce a bearing
of JIS type number 6206 (comparative example A). It is lapped by a thickness of 0.25
mm.
[0187] The test is conducted in the following conditions: A bearing of JIS type number 6206
produced as described above undergoes a fatigue test such that it experiences a maximum
contact pressure Pmax of 3.2 GPa and is rotated at 2000 rpm, using a lubricant of
turbine oil VG68 (clean oil) circularly fed, and thus tested at room temperature.
A vibration detector is employed to monitor how the bearing in operation vibrates,
and after the bearing has a rolling element damaged when the bearing's vibration exceeds
a predetermined value, the test is stopped, and a period of time having elapsed since
the bearing started to operate until the test is stopped is recorded as the bearing's
life. Note that 15 bearings for each example of the present invention and the comparative
example are tested and their L
10 lives are calculated and evaluated for durability by a life ratio in comparison with
comparative example A.
Table 3
|
Working Thickness (mm) |
L10 Life (Time) |
Life Ratio |
Ex. A |
0.05 |
6492 |
3.19 |
Ex. B |
0.10 |
6387 |
3.14 |
Ex. C |
0.15 |
6404 |
3.15 |
Ex. D |
0.20 |
3985 |
1.96 |
Ex. E |
0.30 |
4048 |
1.99 |
Ex. F |
0.40 |
3945 |
1.94 |
Ex. G |
0.50 |
3069 |
1.51 |
Ex. H |
0.60 |
867 |
0.43 |
Comp. Ex. A |
0.25 |
2036 |
1.00 |
[0188] Table 3 shows a result of testing the present example. With reference to table 3,
it can be said that the present example provides bearings all having satisfactory
life with their production costs and the like considered. A working thickness set
to be equal to or smaller than 0.5 mm to provide a rolling element having a surface
with a high density layer remaining therein, i.e., the present invention in examples
D-G, provides a bearing having a life approximately 1.5-2 times that of comparative
example A. Furthermore, a working thickness set to be equal to or smaller than 0.15
mm to provide a rolling element having a surface with a higher density layer remaining
therein, i.e., the present invention in examples A-C, provides a bearing having a
life approximately 3 times that of comparative example A. It is thus confirmed that
a rolling bearing including the present rolling contact member is excellent in durability,
and it has been found that a rolling bearing including the present rolling contact
member with a working thickness set to be equal to or smaller than 0.5 mm to have
a surface with a high density layer remaining therein can have an increased life and
a rolling bearing including the present rolling contact member with a working thickness
set to be equal to or smaller than 0.15 mm to have a surface with a higher density
layer remaining therein can have a further increased life.
Example 4
[0189] Hereinafter the present invention in an example 4 will be described. Specimens formed
of sintered β-sialon having a variety of values z are produced and tested to investigate
the relationship between value z and durability against rolling and sliding contact
fatigue. The test is conducted in the following procedure:
[0190] Initially, specimens to be tested are produced in a method, as will be described
hereinafter. Initially, combustion synthesis is employed to prepare powdery β-sialon
having value z in a range of 0.1-4 and specimens having value z of 0.1-4 are produced
in a method similar to that of producing a torque transmission member for a universal
joint as described above in the fifth embodiment with reference to Fig. 15. More specifically,
they are produced in a method, as follows: Initially, powder of β-sialon in the form
of fine, submicron grains and a sintering additive of aluminum oxide (AKP30 produced
by Sumitomo Chemical Co., Ltd) and yttrium oxide (yttrium oxide grade C produced by
H. C. Starck) are wet-mixed using a ball mill. Subsequently, a spray dryer is used
to granulate the intermediate product to produce granulated powder. The granulated
powder is introduced in a die and thus shaped to be a cylinder, and furthermore, a
cold isostatical press (CIP) is employed to apply pressure to obtain a cylindrically
shaped body.
[0191] Subsequently, the shaped body is preliminarily, pressurelessly sintered and thereafter
undergoes a HIP process in an atmosphere of nitrogen at a pressure of 200 MPa to produce
a sintered cylindrical body. Then, the sintered cylindrical body has an outer circumferential
surface lapped to provide a specimen in the form of a cylinder having a diameter of
ϕ40 mm (examples A-H of the present invention and comparative examples B-C). Furthermore,
for comparison, a specimen formed of silicon nitride, i.e., a specimen having value
z of 0 is also produced in a method similar to that for producing a specimen formed
of β-sialon as described above (comparative example A).
[0192] The test is conducted in the following conditions: Each specimen prepared as described
above is brought into contact with a separately prepared another specimen formed of
bearing steel (JIS SUJ2) (in the form of a cylinder having a diameter of ϕ40 mm and
having been quench-hardened) such that they have their respective axes in parallel
and each specimen experiences a maximum contact pressure Pmax of 2.5 GPa at its outer
circumferential surfaces. Each specimen is rotated at 3000 rpm around the axis and
the other specimen is rotated around the axis to slide relative to each specimen at
a rate of 5%. With a lubricant of turbine oil VG68 (clean oil) fed via a pat, and
at room temperature, each specimen is continuously rotated. A rolling and sliding
fatigue test (a two-cylinder test) is thus conducted. A vibration detector is employed
to monitor how each specimen in operation vibrates, and after each specimen is damaged
when its vibration exceeds a predetermined value, the test is stopped, and a period
of time having elapsed since each specimen started to operate until the test is stopped
is recorded as the specimen's life. Furthermore, after the test is stopped, how each
specimen is damaged is inspected.
Table 4
|
Comp. Ex. A |
Ex. A |
Ex. B |
Ex. C |
Ex. D |
Ex. E |
Ex. F |
Ex. G |
Ex. H |
Comp. Ex. B |
Comp. Ex. C |
Value z |
0 (Silicon Nitride) |
0.1 |
0.5 |
1 |
1.5 |
2 |
2.5 |
3 |
3.5 |
3.8 |
4 |
Life Ratio |
1 |
1.03 |
1.04 |
1.03 |
1.02 |
0.99 |
0.96 |
0.93 |
0.79 |
0.16 |
< 0.05 |
Type of Damage |
Flaked |
Flaked |
Flaked |
Flaked |
Flaked |
Flaked |
Flaked |
Flaked |
Flaked (Also Slightly Worn) |
Flaked (Also Worn) |
Worn |
[0193] Table 4 indicates a result of testing the present example. Table 4 indicates each
example of the present invention and each comparative example having a life represented
as a life ratio in comparison with a comparative example A (silicon nitride) having
a life represented by 1 (one). Furthermore, how a specimen is damaged is recorded
as "flaked" when it has a surface flaked, and as "worn" when it is not flaked and
has a surface worn and accordingly the test is stopped.
[0194] With reference to table 4, examples A-H of the present invention having value z of
0.1 to 3.5 have life comparable to silicon nitride (comparative example A). Furthermore,
examples A-H of the present invention also have damage similar to that of silicon
nitride i.e., "flaked". In contrast, comparative example B having value z exceeding
3.5 and thus deviating from the present invention's range has a significantly reduced
life and its specimen is observed to be worn. More specifically, it is considered
that although comparative example B having value z of 3.8 in the end has its specimen
flaked, the specimen as it is worn has an effect resulting in a significantly reduced
life. Furthermore, comparative example C having value z of 4 has its specimen significantly
worn in a significantly short period of time, and thus significantly impaired in durability.
[0195] Thus for value z in a range of 0.1 to 3.5 a specimen formed of sintered sialon is
substantially equivalent in durability to a specimen formed of sintered silicon nitride.
For value z exceeding 3.5, in contrast, a specimen is wearable, which results in significantly
reduced durability against rolling and sliding contact fatigue. Furthermore, it has
been clarified that increased value z changes a cause of damage to a specimen formed
of β-sialon from "flaked" to "worn" and thus contributes to significantly reduced
durability against rolling and sliding contact fatigue. Thus it has been confirmed
that value z in a range of 0.1 to 3.5 allows a universal joint to be provided that
includes a torque transmission member formed of a sintered β-sialon inexpensive and
capable of reliably ensuring sufficient durability.
[0196] Note that with reference to table 4 example H of the present invention having value
z exceeding 3, more specifically, value z of 3.5, has its specimen slightly worn and
also provides a life shorter than examples A-G of the present invention: It can be
said therefrom that to more reliably ensure sufficient durability, value z equal to
or smaller than 3 is desirable.
[0197] Furthermore, it can be seen from the above test result that, to obtain durability
(or life) equivalent to that of a torque transmission member formed of silicon nitride,
value z equal to or smaller than 2 is preferable, and value z equal to or smaller
than 1.5 is more preferable. Furthermore, when combustion synthesis is adopted in
a production process and accordingly, facilitating preparation of powdery β-sialon
is considered, value z equal to or larger than 0.5 is preferable, as a reaction caused
by a self heating effect can sufficiently be expected.
Example 5
[0198] Hereinafter the present invention in an example 5 will be described. A test is conducted
to confirm the durability of a torque transmission member for a universal joint in
accordance with the present invention against rolling and sliding contact fatigue.
The test is conducted in the following procedure:
[0199] Initially, a specimen to be tested is produced in a method, as will be described
hereinafter. Initially, combustion synthesis is employed to prepare powdery β-sialon
(product name: Meramix, produced by Isman J Corporation) having a composition of Si
5AlON
7, and therefrom a specimen in the form of a cylinder having a diameter of ϕ40 mm is
produced in a method similar to that of producing a torque transmission member for
a universal joint, as described in the seventh embodiment with reference to Fig. 20.
More specifically, it is produced in a method, as follows: Initially, powder of β-sialon
in the form of fine, submicron grains and a sintering additive of aluminum oxide (AKP30
produced by Sumitomo Chemical Co., Ltd) and yttrium oxide (yttrium oxide grade C produced
by H. C. Starck) are wet-mixed using a ball mill. Subsequently, a spray dryer is used
to granulate the intermediate product to produce granulated powder. The granulated
powder is introduced in a die and thus shaped to be a cylinder, and furthermore, a
cold isostatical press (CIP) is employed to apply pressure to obtain a cylindrically
shaped body.
[0200] Then the shaped body is subjected to green body forming so that after it is sintered
it has a predetermined working thickness. Subsequently the shaped body is heated in
an atmosphere of nitrogen of a pressure of 0.4 MPa to 1650°C and thus sintered to
produce a sintered cylindrical body. Then the sintered cylindrical body has an outer
circumferential surface lapped to provide a specimen in the form of a cylinder having
a diameter of ϕ40 mm. Herein, the sintered cylindrical body is lapped to have a thickness
(or a working thickness) removed in 8 levels to produce 8 types of specimens (examples
A-H of the present invention). In contrast, for comparison, silicon nitride and a
sintering additive are used to provide a powdery source material which is in turn
pressure-sintered to provide a sintered cylindrical body which is in turn lapped,
similarly as described above, to produce a specimen in the form of a cylinder having
a diameter of ϕ40 mm (comparative example A). It is lapped by a thickness of 0.25
mm.
[0201] The test is conducted in the following conditions: Each specimen prepared as described
above is brought into contact with a separately prepared another specimen formed of
bearing steel (JIS SUJ2) (in the form of a cylinder having a diameter of ϕ40 mm and
having been quench-hardened) such that they have their respective axes in parallel
and each specimen experiences a maximum contact pressure Pmax of 2.5 GPa at its outer
circumferential surfaces. Each specimen is rotated at 3000 rpm around the axis and
the other specimen is rotated around the axis to slide relative to each specimen at
a rate of 5%. With a lubricant of turbine oil VG68 (clean oil) fed via a pat, and
at room temperature, each specimen is continuously rotated. A rolling and sliding
fatigue test (a two-cylinder test) is thus conducted. A vibration detector is employed
to monitor how each specimen in operation vibrates, and after each specimen is damaged
when its vibration exceeds a predetermined value, the test is stopped, and a period
of time having elapsed since each specimen started to operate until the test is stopped
is recorded as the specimen's life. Note that 8 specimens for each example of the
present invention and the comparative example are tested and their average lives are
calculated and evaluated for durability by a life ratio in comparison with comparative
example A.
Table 5
|
Working Thickness (mm) |
Life (Time) |
Life Ratio |
Ex. A |
0.05 |
1789 |
5.08 |
Ex. B |
0.10 |
1762 |
5.01 |
Ex. C |
0.15 |
1783 |
5.07 |
Ex. D |
0.20 |
1068 |
3.03 |
Ex. E |
0.30 |
957 |
2.72 |
Ex. F |
0.40 |
829 |
2.36 |
Ex. G |
0.50 |
713 |
2.03 |
Ex. H |
0.60 |
321 |
0.91 |
Comp. Ex. A |
0.25 |
352 |
1.00 |
[0202] Table 5 shows a result of testing the examples. With reference to table 5, it can
be said that the examples of the present invention provide specimens all providing
satisfactory life with their production costs and the like considered. A working thickness
set to be equal to or smaller than 0.5 mm to provide a specimen having a surface with
a high density layer remaining therein, i.e., the present invention in examples D-G,
allows the specimen to have a life approximately 2-3 times that of comparative example
A. Furthermore, a working thickness set to be equal to or smaller than 0.15 mm to
provide a specimen having a surface with a higher density layer remaining therein,
i.e., the present invention in examples A-C, allows the specimen to have a life approximately
5 times that of comparative example A. It is thus considered therefrom that a universal
joint including a torque transmission member for the universal joint in accordance
with the present invention is excellent in durability, and that the torque transmission
member for the universal joint with a working thickness set to be equal to or smaller
than 0.5 mm to have a surface with a high density layer remaining therein can provide
an increased life and the torque transmission member for the universal joint with
a working thickness set to be equal to or smaller than 0.15 mm to have a surface with
a higher density layer remaining therein can provide a further increased life.
[0203] It should be understood that the embodiments and examples disclosed herein are illustrative
and non-restrictive in any respect. The scope of the present invention is defined
by the terms of the claims, rather than the description above, and is intended to
include any modifications within the scope and meaning equivalent to the terms of
the claims.
INDUSTRIAL APPLICABILITY
[0204] The present rolling bearing, hub unit, rolling contact member and method of producing
the same are advantageously applicable to rolling bearings, hub units adopting for
a component a sintered body containing β-sialon as a main component, rolling contact
members formed of a sintered body containing β-sialon as a main component, and methods
of producing the same. Furthermore the present universal joint, torque transmission
member for the universal joint, and method of producing the same are advantageously
applicable to universal joints adopting for a component a sintered body containing
β-sialon as a main component, torque transmission members for universal joints, formed
of a sintered body containing β-sialon as a main component, and methods of producing
the same.
1. A rolling bearing (1, 2) comprising:
a race member (11, 12, 21); and
a plurality of rolling elements (13, 23) disposed in contact with said race member
(11, 12, 21) on an annular raceway, said rolling element (13, 23) being configured
of a sintered body that contains as a main component a β-sialon represented by a compositional
formula of Si6-ZAlZOZN8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity.
2. A rolling bearing (1, 2) comprising:
a race member (11, 12, 21); and
a plurality of rolling elements (13, 23) disposed in contact with said race member
(11, 12, 21) on an annular raceway, said rolling element (13, 23) being configured
of a sintered body that contains as a main component a β-sialon represented by a compositional
formula of Si6-ZAlZOZN8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an impurity.
3. A hub unit (3) posed between a vehicular wheel and a vehicular body and supporting
said vehicular wheel relative to said vehicular body rotatably, comprising:
an outer member (31) having an inner circumferential surface having an annular raceway
surface (31A1, 31A2);
an inner member (32, 33) disposed radially inner than said outer member (31) and having
an annular raceway surface (32A, 33A) opposite to said raceway surface (31A1, 31A2)
of said outer member (31); and
a plurality of rolling elements (34) disposed in contact with said raceway surface
(31A1, 31A2) of said outer member (31) and said raceway surface (32A, 33A) of said
inner member (32, 33) on an annular raceway, said rolling element (34) being configured
of a sintered body that contains as a main component a β-sialon represented by a compositional
formula of Si6-ZAlZOZN8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity.
4. A hub unit (3) posed between a vehicular wheel and a vehicular body and supporting
said vehicular wheel relative to said vehicular body rotatably, comprising:
an outer member (31) having an inner circumferential surface having an annular raceway
surface (31A1, 31A2);
an inner member (32, 33) disposed radially inner than said outer member (31) and having
an annular raceway surface (32A, 33A) opposite to said raceway surface (31A1, 31A2)
of said outer member (31); and
a plurality of rolling elements (34) disposed in contact with said raceway surface
(31A1, 31A2) of said outer member (31) and said raceway surface (32A, 33A) of said
inner member (32, 33) on an annular raceway, said rolling element (34) being configured
of a sintered body that contains as a main component a β-sialon represented by a compositional
formula of Si6-ZAlZOZN8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an impurity.
5. A rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34) in a rolling bearing
(1, 2, 3), the rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34) being one
of a race member (11, 12, 21, 31, 32, 33) and a rolling element (13, 23, 34) disposed
in contact with said race member (11, 12, 21, 31, 32, 33) on an annular raceway, the
rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34) being configured of a
sintered body that contains as a main component a β-sialon represented by a compositional
formula of Si6-ZAlZOZN8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity, the rolling
contact member (11, 12, 13, 21, 23, 31, 32, 33, 34) having a rolling contact surface
(11A, 12A, 13A, 21A, 23A, 31A1, 31A2, 32A, 33A, 34A) serving as a surface contacting
another rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34), said rolling
contact surface (11A, 12A, 13A, 21A, 23A, 31A1, 31A2, 32A, 33A, 34A) being included
in a portion having a high density layer (11B, 11D, 12B, 12D, 13B, 13D, 21B, 21D,
23B, 23D, 31B, 31D, 32B, 32D, 33B, 33D, 34B, 34D) higher in density than an inner
portion (11C, 12C, 13C, 21C, 23C, 31C,32C,33C,34C).
6. The rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34) according to claim
5, wherein when said high density layer (11B, 11D, 12B, 12D, 13B, 13D, 21B, 21D, 23B,
23D, 31B, 31D, 32B, 32D, 33B, 33D, 34B, 34D) is observed in cross section with an
optical microscope with oblique illumination, said layer exhibits a portion observed
as a portion white in color having an area ratio equal to or smaller than 7%.
7. The rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34) according to claim
5, wherein said high density layer (11B, 11D, 12B, 12D, 13B, 13D, 21B, 21D, 23B, 23D,
31B, 31D, 32B, 32D, 33B, 33D, 34B, 34D) has a surface included in a portion having
a higher density layer (11D, 12D, 13D, 21D, 23D, 31D, 32D, 33D, 34D) higher in density
than another portion of said high density layer (11B, 11D, 12B, 12D, 13B, 13D, 21B,
21D, 23B, 23D, 31B, 31D, 32B, 32D, 33B, 33D, 34B, 34D).
8. The rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34) according to claim
7, wherein when said higher density layer (11D, 12D, 13D, 21D, 23D, 31D, 32D, 33D,
34D) is observed in cross section with an optical microscope with oblique illumination,
said layer exhibits a portion observed as a portion white in color having an area
ratio equal to or smaller than 3.5%.
9. A rolling bearing (1, 2, 3) comprising:
a race member (11, 12, 21, 31, 32, 33); and
a plurality of rolling elements (13, 23, 34) disposed in contact with said race member
(11, 12, 21, 31, 32, 33) on an annular raceway, at least one of said race member (11,
12, 21, 31, 32, 33) and said rolling element (13, 23, 34) being the rolling contact
member (11, 12, 13, 21, 23, 31, 32, 33, 34) of claim 5.
10. A rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34) in a rolling bearing
(1, 2, 3), the rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34) being one
of a race member (11, 12, 21, 31, 32, 33) and a rolling element (13, 23, 34) disposed
in contact with said race member (11, 12, 21, 31, 32, 33) on an annular raceway, the
rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34) being configured of a
sintered body that contains as a main component a β-sialon represented by a compositional
formula of Si6-ZAlZOZN8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an impurity, the rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34) having
a rolling contact surface (11A, 12A, 13A, 21A, 23A, 31A1, 31A2, 32A, 33A, 34A) serving
as a surface contacting another rolling contact member (11, 12, 13, 21, 23, 31, 32,
33, 34), said rolling contact surface (11A, 12A, 13A, 21A, 23A, 31A1, 31A2, 32A, 33A,
34A) being included in a portion having a high density layer (11B, 11D, 12B, 12D,
13B, 13D, 21B, 21D, 23B, 23D, 31B, 31D, 32B, 32D, 33B, 33D, 34B, 34D) higher in density
than an inner portion (11C, 12C, 13C, 21C, 23C, 31C, 32C, 33C, 34C).
11. The rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34) according to claim
10, wherein when said high density layer (11B, 11D, 12B, 12D, 13B, 13D, 21B, 21D,
23B, 23D, 31B, 31D, 32B, 32D, 33B, 33D, 34B, 34D) is observed in cross section with
an optical microscope with oblique illumination, said layer exhibits a portion observed
as a portion white in color having an area ratio equal to or smaller than 7%.
12. The rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34) according to claim
10, wherein said high density layer (11B, 11D, 12B, 12D, 13B, 13D, 21B, 21D, 23B,
23D, 31B, 31D, 32B, 32D, 33B, 33D, 34B, 34D) has a surface included in a portion having
a higher density layer (11D, 12D, 13D, 21D, 23D, 31D, 32D, 33D, 34D) higher in density
than another portion of said high density layer (11B, 11D, 12B, 12D, 13B, 13D, 21B,
21D, 23B, 23D, 31B, 31D, 32B, 32D, 33B, 33D, 34B, 34D).
13. The rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34) according to claim
12, wherein when said higher density layer (11D, 12D, 13D, 21D, 23D, 31D, 32D, 33D,
34D) is observed in cross section with an optical microscope with oblique illumination,
said layer exhibits a portion observed as a portion white in color having an area
ratio equal to or smaller than 3.5%.
14. A rolling bearing (1, 2, 3) comprising:
a race member (11, 12, 21, 31, 32, 33); and
a plurality of rolling elements (13, 23, 34) disposed in contact with said race member
(11, 12, 21, 31, 32, 33) on an annular raceway, at least one of said race member (11,
12, 21, 31, 32, 33) and said rolling element (13, 23, 34) being the rolling contact
member (11, 12, 13, 21, 23, 31, 32, 33, 34) of claim 10.
15. A method of producing a rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34)
in a rolling bearing (1, 2, 3), said rolling contact member (11, 12, 13, 21, 23, 31,
32, 33, 34) being one of a race member (11, 12, 21, 31, 32, 33) and a rolling element
(13, 23, 34) disposed in contact with said race member (11, 12, 21, 31, 32, 33) on
an annular raceway, comprising the steps of:
preparing a powdery source material that contains as a main component a β-sialon represented
by a compositional formula of Si6-ZAlZOZN8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity;
shaping said powdery source material generally into a geometry of said rolling contact
member (11, 12, 13, 21, 23, 31, 32, 33, 34) to provide a shaped body; and
sintering said shaped body at a pressure equal to or smaller than 1 MPa.
16. The method of producing a rolling contact member (11, 12, 13, 21, 23, 31, 32, 33,
34) according to claim 15, wherein the step of sintering said shaped body includes
sintering said shaped body in a range of 1550°C to 1800°C.
17. The method of producing a rolling contact member (11, 12, 13, 21, 23, 31, 32, 33,
34) according to claim 15, wherein the step of sintering said shaped body includes
sintering said shaped body in one of an atmosphere of an inert gas and an atmosphere
of a gaseous mixture of nitrogen and oxygen.
18. The method of producing a rolling contact member (11, 12, 13, 21, 23, 31, 32, 33,
34) according to claim 15, further comprising the step of forming a surface of said
shaped body before sintering said shaped body.
19. The method of producing a rolling contact member (11, 12, 13, 21, 23, 31, 32, 33,
34) according to claim 15, further comprising the step of working a surface of said
shaped body sintered, to remove a portion including said surface, the step of working
removing said shaped body by a thickness equal to or smaller than 150 µm.
20. A method of producing a rolling contact member (11, 12, 13, 21, 23, 31, 32, 33, 34)
in a rolling bearing (1, 2, 3), said rolling contact member (11, 12, 13, 21, 23, 31,
32, 33, 34) being one of a race member (11, 12, 21, 31, 32, 33) and a rolling element
(13, 23, 34) disposed in contact with said race member (11, 12, 21, 31, 32, 33) on
an annular raceway, comprising the steps of:
preparing a powdery source material that contains as a main component a β-sialon represented
by a compositional formula of Si6-ZAlZOZN8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an impurity;
shaping said powdery source material generally into a geometry of said rolling contact
member (11, 12, 13, 21, 23, 31, 32, 33, 34) to provide a shaped body; and
sintering said shaped body at a pressure equal to or smaller than 1 MPa.
21. The method of producing a rolling contact member (11, 12, 13, 21, 23, 31, 32, 33,
34) according to claim 20, wherein the step of sintering said shaped body includes
sintering said shaped body in a range of 1550°C to 1800°C.
22. The method of producing a rolling contact member (11, 12, 13, 21, 23, 31, 32, 33,
34) according to claim 20, wherein the step of sintering said shaped body includes
sintering said shaped body in one of an atmosphere of an inert gas and an atmosphere
of a gaseous mixture of nitrogen and oxygen.
23. The method of producing a rolling contact member (11, 12, 13, 21, 23, 31, 32, 33,
34) according to claim 20, further comprising the step of forming a surface of said
shaped body before sintering said shaped body.
24. The method of producing a rolling contact member (11, 12, 13, 21, 23, 31, 32, 33,
34) according to claim 20, further comprising the step of working a surface of said
shaped body sintered, to remove a portion including said surface, the step of working
removing said shaped body by a thickness equal to or smaller than 150 µm.
25. A universal joint (100, 200) comprising:
a race member (112, 222) connected to a first shaft member (116, 226);
a torque transmission member (113, 223) arranged in contact with said race member
(112, 222) rollably on a surface (112A, 222A) of said race member (112, 222); and
a second shaft member (115, 225) connected via said torque transmission member (113,
223) and said race member (112, 222) to said first shaft member (116, 226), the universal
joint (100, 200) transmitting rotation transmitted to one of said first shaft member
(116, 226) and said second shaft member (115, 225) about an axis to the other of said
first shaft member (116, 226) and said second shaft member (115, 225), said torque
transmission member (113, 223) being configured of a sintered body that contains as
a main component a β-sialon represented by a compositional formula of Si6-ZAlZOZN8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity.
26. A universal joint (100, 200) comprising:
a race member (112, 222) connected to a first shaft member (116, 226);
a torque transmission member (113, 223) arranged in contact with said race member
(112, 222) rollably on a surface (112A, 222A) of said race member (112, 222); and
a second shaft member (115, 225) connected via said torque transmission member (113,
223) and said race member (112, 222) to said first shaft member (116, 226), the universal
joint (100, 200) transmitting rotation transmitted to one of said first shaft member
(116, 226) and said second shaft member (115, 225) about an axis to the other of said
first shaft member (116, 226) and said second shaft member (115, 225), said torque
transmission member (113, 223) being configured of a sintered body that contains as
a main component a β-sialon represented by a compositional formula of Si6-ZAlZOZN8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an impurity.
27. A torque transmission member (113, 223) for a universal joint, provided in a universal
joint (100, 200) between a race member (112, 222) connected to a first shaft member
(116, 226) and a second shaft member (115, 225) rollably and slidably and transmitting
rotation transmitted to one of said first shaft member (116, 226) and said second
shaft member (115, 225) about an axis to the other of said first shaft member (116,
226) and said second shaft member (115, 225), the torque transmission member (113,
223) being configured of a sintered body that contains as a main component a β-sialon
represented by a compositional formula of Si6-ZAlZOZN8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity, the torque
transmission member (113, 223) having a contact surface (113A, 223A) serving as a
surface contacting another member, said surface (113A, 223A) being included in a portion
having a high density layer (113B, 113D, 223B, 223D) higher in density than an inner
portion (113C, 223C).
28. The torque transmission member (113, 223) for a universal joint according to claim
27, wherein when said high density layer (113B, 113D, 223B, 223D) is observed in cross
section with an optical microscope with oblique illumination, said layer exhibits
a portion observed as a portion white in color having an area ratio equal to or smaller
than 7%.
29. The torque transmission member (113, 223) for a universal joint according to claim
27, wherein said high density layer (113B, 113D, 223B, 223D) has a surface included
in a portion having a higher density layer (113D, 223D) higher in density than another
portion of said high density layer (113B, 113D, 223B, 223D).
30. The torque transmission member (113, 223) for a universal joint according to claim
29, wherein when said higher density layer (113D, 223D) is observed in cross section
with an optical microscope with oblique illumination, said layer exhibits a portion
observed as a portion white in color having an area ratio equal to or smaller than
3.5%.
31. A universal joint (100, 200) comprising:
a race member (112, 222) connected to a first shaft member (116, 226);
a torque transmission member (113, 223) arranged in contact with said race member
(112, 222) rollably and slidably on a surface (112A, 222A) of said race member (112,
222); and
a second shaft member (115, 225) connected via said torque transmission member (113,
223) and said race member (112, 222) to said first shaft member (116, 226), the universal
joint (100, 200) transmitting rotation transmitted to one of said first shaft member
(116, 226) and said second shaft member (115, 225) about an axis to the other of said
first shaft member (116, 226) and said second shaft member (115, 225), said torque
transmission member (113, 223) being the torque transmission member (113, 223) of
claim 27 for a universal joint.
32. A torque transmission member (113, 223) for a universal joint, provided in a universal
joint (100, 200) between a race member (112, 222) connected to a first shaft member
(116, 226) and a second shaft member (115, 225) rollably and slidably and transmitting
rotation transmitted to one of said first shaft member (116, 226) and said second
shaft member (115, 225) about an axis to the other of said first shaft member (116,
226) and said second shaft member (115, 225), the torque transmission member (113,
223) being configured of a sintered body that contains as a main component a β-sialon
represented by a compositional formula of Si6-ZAlZOZN8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an impurity, the torque transmission member (113, 223) having a contact surface (113A,
223A) serving as a surface contacting another member, said surface (113A, 223A) being
included in a portion having a high density layer (113B, 113D, 223B, 223D) higher
in density than an inner portion (113C, 223C).
33. The torque transmission member (113, 223) for a universal joint according to claim
32, wherein when said high density layer (113B, 113D, 223B, 223D) is observed in cross
section with an optical microscope with oblique illumination, said layer exhibits
a portion observed as a portion white in color having an area ratio equal to or smaller
than 7%.
34. The torque transmission member (113, 223) for a universal joint according to claim
32, wherein said high density layer (113B, 113D, 223B, 223D) has a surface included
in a portion having a higher density layer (113D, 223D) higher in density than another
portion of said high density layer (113B, 113D, 223B, 223D).
35. The torque transmission member (113, 223) for a universal joint according to claim
34, wherein when said higher density layer (113D, 223D) is observed in cross section
with an optical microscope with oblique illumination, said layer exhibits a portion
observed as a portion white in color having an area ratio equal to or smaller than
3.5%.
36. A universal joint (100, 200) comprising:
a race member (112, 222) connected to a first shaft member (116, 226);
a torque transmission member (113, 223) arranged in contact with said race member
(112, 222) rollably and slidably on a surface (112A, 222A) of said race member (112,
222); and
a second shaft member (115, 225) connected via said torque transmission member (113,
223) and said race member (112, 222) to said first shaft member (116, 226), the universal
joint (100, 200) transmitting rotation transmitted to one of said first shaft member
(116, 226) and said second shaft member (115, 225) about an axis to the other of said
first shaft member (116, 226) and said second shaft member (115, 225), said torque
transmission member (113, 223) being the torque transmission member (113, 223) of
claim 32 for a universal joint.
37. A method of producing a torque transmission member (113, 223) for a universal joint,
provided in a universal joint (100, 200) between a race member (112, 222) connected
to a first shaft member (116, 226) and a second shaft member (115, 225) rollably and
slidably and transmitting rotation transmitted to one of said first shaft member (116,
226) and said second shaft member (115, 225) about an axis to the other of said first
shaft member (116, 226) and said second shaft member (115, 225), comprising the steps
of:
preparing a powdery source material that contains as a main component a β-sialon represented
by a compositional formula of Si6-ZAlZOZN8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of an impurity;
shaping said powdery source material generally into a geometry of said torque transmission
member (113, 223) for said universal joint to provide a shaped body; and
sintering said shaped body at a pressure equal to or smaller than 1 MPa.
38. The method of producing a torque transmission member (113, 223) for a universal joint
according to claim 37, wherein the step of sintering said shaped body includes sintering
said shaped body in a range of 1550°C to 1800°C.
39. The method of producing a torque transmission member (113, 223) for a universal joint
according to claim 37, wherein the step of sintering said shaped body includes sintering
said shaped body in one of an atmosphere of an inert gas and an atmosphere of a gaseous
mixture of nitrogen and oxygen.
40. The method of producing a torque transmission member (113, 223) for a universal joint
according to claim 37, further comprising the step of forming a surface of said shaped
body before sintering said shaped body.
41. The method of producing a torque transmission member (113, 223) for a universal joint
according to claim 37, further comprising the step of working a surface of said shaped
body sintered, to remove a portion including said surface, the step of working removing
said shaped body by a thickness equal to or smaller than 150 µm.
42. A method of producing a torque transmission member (113, 223) for a universal joint,
provided in a universal joint (100, 200) between a race member (112, 222) connected
to a first shaft member (116, 226) and a second shaft member (115, 225) rollably and
slidably and transmitting rotation transmitted to one of said first shaft member (116,
226) and said second shaft member (115, 225) about an axis to the other of said first
shaft member (116, 226) and said second shaft member (115, 225), comprising the steps
of:
preparing a powdery source material that contains as a main component a β-sialon represented
by a compositional formula of Si6-ZAlZOZN8-Z and satisfying 0.1 ≤ z ≤ 3.5 and has a remainder formed of a sintering additive and
an impurity;
shaping said powdery source material generally into a geometry of said torque transmission
member (113, 223) for said universal joint to provide a shaped body; and
sintering said shaped body at a pressure equal to or smaller than 1 MPa.
43. The method of producing a torque transmission member (113, 223) for a universal joint
according to claim 42, wherein the step of sintering said shaped body includes sintering
said shaped body in a range of 1550°C to 1800°C.
44. The method of producing a torque transmission member (113, 223) for a universal joint
according to claim 42, wherein the step of sintering said shaped body includes sintering
said shaped body in one of an atmosphere of an inert gas and an atmosphere of a gaseous
mixture of nitrogen and oxygen.
45. The method of producing a torque transmission member (113, 223) for a universal joint
according to claim 42, further comprising the step of forming a surface of said shaped
body before sintering said shaped body.
46. The method of producing a torque transmission member (113, 223) for a universal joint
according to claim 42, further comprising the step of working a surface of said shaped
body sintered, to remove a portion including said surface, the step of working removing
said shaped body by a thickness equal to or smaller than 150 µm.